Encoding apparatus, decoding apparatus, encoding method and decoding method

ABSTRACT

By combining a plurality of encoding methods actively, an encoding efficiency is enhanced. The first encoder encodes a result of determination whether a prediction error is zero or not. The second encoder encodes the prediction error unless the prediction error is zero. The third encoder encodes the prediction error regardless of whether the prediction error is zero or not. The mode determinator determines the encoding mode, and the encoding controller selectively operates the first encoder, the second encoder, and the third encoder according to the encoding mode determined.

This application is a divisional of Application No. 08/952,723, now U.S.Pat. No. 6,188,793 filed on Nov. 19, 1997. Application No. 08/952,723 isthe national phase of PCT International Application No. PCT/JP97/00768filed on Mar. 12, 1997 under 35 U.S.C. §371. The entire contents of eachof the above-identified applications are hereby incorporated byreference.

TECHNICAL FIELD

The present invention relates to an encoding apparatus, a decodingapparatus and their methods for encoding and decoding pictureinformation generated by and used in a facsimile machine, a scanner, anda computer. More specifically, the present invention relates to anencoding apparatus and a decoding apparatus having two types of encodingand decoding systems for efficiently encoding and decoding pictureinformation by switching between the two types of encoding and decodingsystems. Further, the present invention relates to an encoding methodand a decoding method for encoding and decoding picture informationefficiently. The present invention also relates to a picture processingapparatus having an encoding apparatus and a decoding apparatusaccording to the present invention. The present invention also relatesto a picture processing apparatus for implementing an encoding methodand a decoding method according to the present invention.

BACKGROUND ART

Related Art 1.

FIG. 66 is a block diagram showing a conventional encoding apparatus.

In FIG. 66, reference numeral 901 indicates a picture element memory forreceiving, storing, and outputting the value of a picture element to beencoded (which will be referred to as an encoding picture element, orsimply as a picture element) and for outputting the value of at leastone encoded picture element already stored in the picture element memoryand adjacent to the encoding picture element as the value of a referencepicture element.

Reference numeral 907 indicates a predictor for calculating theprediction value for the encoding picture element by referring to thevalue of the at least one reference picture element.

Reference numeral 931 indicates a prediction error calculator fordetermining the prediction error by subtracting the prediction valuecalculated by the predictor 907 from the value of the encoding pictureelement.

Reference numeral 908 indicates an encoder for encoding the predictionerror between the value of the encoding picture element and theprediction value calculated by the predictor 907, and for outputtingcodewords.

Reference numeral 910 indicates a code buffer for receiving thecodewords supplied from the encoder 908 and for outputting a sequence ofthe codewords as a code in order of the received codewords.

Next, an operation of the conventional encoding apparatus is explained.

The predictor 907 calculates the prediction value from the value of theat least one reference picture element. The calculation method may beimplemented in accordance with a predetermined prediction function or byreferring to a reference table. The encoder 908 encodes the predictionerror (−255˜+255, inclusive of zero, in the case of one picture elementbeing represented by eight bits) which has been obtained by subtractingthe calculated prediction value from the value of an encoding pictureelement by using a predetermined codeword table.

Related Art 2.

As another conventional related art, conversion of the prediction errorsfor encoding picture elements and picture elements to be decoded intobinary symbol sequences, and encoding and decoding the binary symbolsequences are known. As one of the encoding and decoding methods forbinary symbols, the encoding and decoding method disclosed in JapanesePatent Registered No. 1251403 will be described herein.

According to this encoding and decoding method, as shown in FIG. 67, onecodeword is allotted to a binary symbol sequence composed of one binarysymbol or a plurality of binary symbols. The term “encoding” is used inthis specification to mean an operation for determining and allotting acodeword to a sequence of a certain number (which will be hereinafterreferred to as the code order) of binary “0” symbols (More ProbableSymbols abbreviated to MPSs) or binary “1” symbols (Less Probable Symbolabbreviated to LPSs) occurred, and for outputting the codeword therefor.At the time of encoding, the number of MPSs consecutively occurred iscounted by an MPS counter (not shown) inside (or outside) the encoder.The counted value of MPSs is stored in an MPS memory (not shown), andthe state numbers of binary symbol sequences (to be described hereafter)are stored in a state-number memory (not shown). The code order may bean integer greater than zero. However, it is assumed herein that thecode order is restricted to 2^(n) (the n-th power of 2). When the numberof MPSs consecutively occurred (the count of the MPS counter) has becomeequal to the code order 2^(n), one-bit codeword “0” is allotted to theMPSs. On the other hand, when an LPS has occurred before the number ofMPSs consecutively occurred becomes equal to the code order, the numberof the MPSs consecutively occurred after outputting the latest codewordbefore occurring the LPS is expressed in terms of n-bit binary symbols,and, in order to differentiate from the sequence of the MPSs to whichthe codeword “0” is allotted, the codeword “1” is added to the beginningof the n-bit binary symbols. Accordingly, a codeword of (n+1) bits isallotted to the sequence of MPSs plus the LPS differentiating from thesequence of MPSs to which a codeword of “0” is allotted. The unit of abinary symbol sequence to which a codeword is allotted is referred to asa message. After the codeword is determined and output, the MPS counteris reset. A sequence of codewords output in this way constitutes a code.On the other hand, when a code is to be decoded, the code is supplied tothe decoder and divided into individual codewords. Then, a binary symbolsequence is recreated by the decoder, and picture elements arereproduced. In this way, decoding is implemented.

In the aforementioned encoding and decoding method, the code order ischanged so as to represent the appropriate code length in accordancewith the occurrence probability of one of binary symbols estimated frompast data on binary symbol sequences. For this reason, a furtherexcellent encoding efficiency can be obtained.

A first example of the state transition method of determining the codeorder will be described now.

When a binary symbol sequence is encoded or decoded by an encoder or adecoder, the binary symbol sequence belongs to one of the sixteen statesshown in FIG. 68. The code order is determined according to the state towhich each binary symbol sequence belongs. It is assumed herein that theinitial value of the state number for the encoder or the decoder is setto 0. It is also assumed herein that the MPS counter of the encoder orthe decoder is reset at the beginning of the encoding process or thedecoding process. During the encoding process or the decoding process,the encoder or the decoder implements state transition when a codewordhas been determined. When the number of MPSs consecutively occurred in abinary symbol sequence has become equal to the code order of the binarysymbol sequence, the state number of the sequence is increased by one.When an LPS has occurred in a binary symbol sequence before the numberof MPSs consecutively occurred becomes equal to the code order of thebinary symbol sequence, the state number of the sequence is decreased byone. However, when the number of MPSs consecutively occurred in a binarysymbol sequence having the state number 15 has become equal to the codeorder of the binary symbol sequence, or when an LPS has occurred in abinary symbol sequence having the state number 0, the encoder or thedecoder does not implement state transition, and the state numberremains unchanged.

According to a second example of the method of determining the codeorder, there is shown a method in which the numbers of binary symbols“0” and binary symbols “1” which have occurred in a binary symbolsequence, respectively indicated by N(0) and N(1), are counted on boththe transmitting side and the receiving side within the same range (suchas, for example, within one line) so as to calculate the code order ofthe binary symbol sequence, based on the result of the count. The methodof determining the code order, for example, is disclosed in JapaneseUnexamined Patent Publication No. SHO59-27501 (which corresponds toUnited States Patent No. 4191974). The calculation method is expressedby the relation of 2^(n+l) N(1)>N(0)≧2^(n) N(1). In this case, however,the code order 2^(n) which varies with state transition of a binarysymbol sequence is not less than a predetermined minimum value, nor morethan a predetermined maximum value.

It is known that the encoding method shown in FIG. 67 has the followingcharacteristics. Let us assume that a binary information source whoseprobability of binary symbol “0” and whose probability of binary symbol“1” are p, 1−p (p≧½) respectively are encoded in accordance with theencoding method shown in FIG. 67. When the occurrence of the binarysymbols to be encoded may be random, the order n rendering a maximumcode length in each code order minimum fulfills the followingexpression:

{2^(n)/(2^(n)+1)}≦p<{2^(n+1)/(2^(n+1)+1)}

Accordingly, by determining n in accordance with the above expression, asubstantially optimum code can be selected.

Assuming that the number of binary symbols “0” is N(0) and the number ofbinary symbols “1” is N(1), the probability p is expressed as follows:

p=N(0)/{N(0)+N(1)}

Thus the above expression s reduced to as follows:

2^(n) N(1)≦N(0)≦2^(n+1) N(1)

Related Art 3.

Among the conventional encoding apparatuses and the conventionaldecoding apparatuses, there is an encoding apparatus or a decodingapparatus wherein two encoding or decoding modes such as the mode A andthe mode B are provided, for example, and encoding or decoding isimplemented by switching between the mode A and the mode B according tothe decision whether or not a predetermined condition for the value(s)of reference picture element(s) is satisfied. Basically, if the value(s)of reference picture element(s) satisfies a predetermined condition,encoding or decoding is implemented in the mode A. On the other hand, ifthe value(s) of reference picture element(s) does not satisfy apredetermined condition, encoding or decoding is implemented in the modeB. Mode switching may be accomplished, for example, in accordance withthe method described in “The National Assembly 1016 of the Institute ofElectronics and Communication Engineers of Japan held in 1977” as the“run length encoding process according to the encoding start patterns”.As shown in FIG. 69, a picture element X is assumed herein to be apicture element to be encoded or decoded (which will be hereinaftersimply referred to as a picture element). If the values of referencepicture elements a, b, and c adjacent to the picture element X satisfy apredetermined condition “a=b=c”, the picture element X and thesubsequent picture elements are encoded or decoded continuously in themode A until the picture element X becomes “X≈ a prediction value”. Whenthe picture element X occurs that does not coincide with the predictionvalue, the mode A is switched into the mode B. Then, the picture elementX and the subsequent picture elements are encoded or decodedcontinuously in the mode B. When the values of the reference pictureelements a, b, and c satisfy the predetermined condition “a=b=c” again,the mode is switched to the mode A and the subsequent encoding ordecoding picture element is encoded or decoded in the mode A.

Related Art 4.

In the following, encoding process and decoding process of a picture ina conventional picture pick-up apparatus is explained referring todrawings. In this related art, encoding process is performed by apicture compression circuit and decoding process is performed by apicture expansion circuit.

FIG. 70 shows a configuration of the picture compression circuit and thepicture expansion circuit.

In FIG. 70, the picture compression circuit includes a process forimplementing a lossless compression and another process for implementinga lossy compression.

A lossy picture compression means a compressing process where acompressibility of the picture is increased, though a quality ofreproduced picture (reproducibility) is decreased.

On the other hand, a lossless picture compression means a compressingprocess where the quality of reproduced picture (reproducibility) is notdecreased, though a compressibility of the picture is less increasedthan the above lossy picture compression.

A DCT (Discrete Cosine Transform) circuit 951 performs two-dimensionalDCT operation on an input picture to divide the picture intotwo-dimensional spatial frequency components. A quantization circuit 952quantizes a DCT coefficient. An entropy encoder 953 implements Huffmancoding on the quantized DCT coefficient. The lossy picture compressionis performed by the DCT circuit 951, the quantization circuit 952 andthe entropy encoder 953. A predictor 954 predicts data of a certainpicture element by using data of the previous picture element. Anentropy encoder 955 implements Huffman coding of a differential betweenthe picture element and the picture element predicted by the predictor954. In this way, the lossless data compression is implemented by thepredictor 954 and the entropy encoder 955. A switch SW1 selects one ofthe compressing processes: side “a” of the lossless compression; andside “b” of the lossy compression.

The picture expansion circuit includes a process for implementing alossless expansion and a process for implementing lossy expansion. Anentropy decoder 956 and a decoder 957 decode the reversibly compresseddata by an inverse operation of the entropy encoder 955 and thepredictor 954. An entropy decoder 958, a dequantization circuit 959 andan inverse DCT circuit 960 decode the compressed data by an inverseoperation of the DCT circuit 951, the quantization circuit 952 and theentropy encoder 953. A switch SW2 selects one of the expandingprocesses: side “a” of the lossless expansion; and side “b” of the lossyexpansion.

The conventional encoding apparatus which has been described as therelated art 1 encodes a prediction error by referring to a predeterminedcodeword table. Generally, with regard to the picture information, thestatistical characteristic of the picture information displayed on ascreen varies greatly depending on the part on the screen. In otherwords, it is known that it occurs that prediction for some part of thepicture information displayed on the screen tends to be correct whileother part of the picture information displayed on the screen often hasgreat prediction errors. Although the statistical characteristic of thepicture information displayed on the screen varies, the encodingapparatus according to the first conventional related art implementsencoding by referring to a single codeword table. Thus, it has created aproblem in that an encoding efficiency cannot be enhanced.

On the other hand, the encoding method which has been described as therelated art 2 is a method of implementing encoding by referring to aplurality of codeword tables and dynamically changing the code orderdepending on the occurrence probability of the MPS. Consequently, if thestatistical characteristic of picture information displayed variesgreatly, a more excellent encoding efficiency will be provided with thisencoding system than with the encoding apparatus which has beendescribed as the first conventional related art. However, even by usingthe encoding method according to related art 2, when at least onecodeword is allotted to a prediction error for each encoding pictureelement, at least one-bit code amount is required for each pictureelement regardless of whether or not the prediction has proved to becorrect (or no prediction error has been produced). Allotting a one-bitor more bits of codeword to a prediction error although the predictionprobability exceeds ½ means that the actual code amount required isgreater than the theoretical minimum code amount (entropy) for theprediction error. In other words, it means that an encoding efficiencyis reduced.

According to the aforementioned related art 4, the picture compressioncircuit (encoding apparatus) and the picture expansion circuit (decodingapparatus) are configured as shown in FIG. 70. The DCT circuit, thequantization circuit and the entropy encoder implement lossy picturecompression and lossy picture expansion. On the other hand, thepredictor and the entropy encoder implement lossless picture compressionand lossless picture expansion. In this way, the conventional picturepick-up apparatus switches the lossless picture compression circuit andthe lossy picture compression circuit according to the condition. In thepicture pick-up apparatus, it is mostly required to increase thecompressibility of the picture without decreasing the quality of thereproduced picture (reproducibility). Particularly, in the art of adigital camera, the above requests have been highly demanded these daysso as to store the picked-up signals in the storage medium and todisplay the picked-up signals on the monitor. Input information ofpicture has been increasing because of a large number of pictureelements of input picture, color input picture, and multiple gradationof input picture. There is a problem that the conventional pictureprocessing apparatus cannot supply enough compressibility of picture incase of storing such information of picture in a limited capacity of thestorage medium.

On handling multimedia information, picture information is transmitted,displayed, or stored together with other information such as audioinformation, or character information. Picture information occupieshigher ratio than other information among such multimedia information,and these days it is required that the compressibility of picture isfurther increased.

OBJECTS OF THE INVENTION

The present invention has been made to solve the above-mentionedproblems. It is therefore an object of the present invention to providean encoding apparatus and a decoding apparatus which can implementencoding and decoding picture information efficiently.

Further, it is another object of the present invention to provide anencoding method and a decoding method for encoding and decoding pictureinformation efficiently by actively switching between different types ofencoding systems and decoding systems.

It is a further object of the present invention to provide an encodingapparatus and a decoding apparatus which can be produced in a smallersize and constructed easily even when encoding and decoding pictureinformation are to be efficiently implemented by actively switchingbetween different types of encoding systems and decoding systems.

Further, it is also an object of the present invention to provide apicture processing apparatus having the above-mentioned encodingapparatus and the above-mentioned decoding apparatus.

Still further, it is also an object of the present invention to providea picture processing apparatus for implementing the above-mentionedencoding method and the above-mentioned decoding method.

It is an object of the present invention to provide an pictureprocessing apparatus for implementing a lossless picture compressionwith higher compressibility than the lossless picture compressionimplemented by the conventional picture processing apparatus.

SUMMARY OF THE INVENTION

An decoding apparatus according to the present invention may comprise:

a picture element memory for receiving and storing a picture elementhaving a value within a predetermined range as an encoding pictureelement, outputting the value of the encoding picture element, and foroutputting a value of an encoded picture element adjacent to theencoding picture element as the value of a reference picture element;

a mode determinator for selecting one of a specific encoding mode and anencoding mode other than the specific encoding mode from a plurality ofpredefined encoding modes for the encoding picture element based on thevalue of the reference picture element;

a first encoding section for predicting the value of the encodingpicture element, determining whether the prediction is correct, encodingthe value of the encoding picture element based on a result of thedetermination, and for outputting a codeword for the encoding pictureelement;

a second encoding section for predicting the value of the encodingpicture element, encoding the value of the encoding picture elementwithout determining whether the prediction is correct, and foroutputting a codeword for the encoding picture element; and

an encoding controller for selectively operating the first encodingsection and the second encoding section based on one of the specificencoding mode and the encoding mode other than the specific encodingmode selected by the mode determinator.

The first encoding section may comprise:

a first predictor for calculating a prediction value of the encodingpicture element based on the value of the reference picture element;

a first prediction error calculator for calculating an error between thevalue of the encoding picture element and the prediction valuecalculated by the first predictor as a prediction error;

a determinator for determinating whether the prediction error calculatedby the first prediction error calculator is a specific value, and foroutputting a result of the determination;

a first encoder for receiving and encoding the result of thedetermination output from the determinator, and for outputting thecodeword for the encoding picture element to be encoded in the selectedspecific encoding mode; and

a second encoder for encoding the prediction error calculated by thefirst prediction error calculator when the prediction error is otherthan the specific value for the encoding picture element to be encodedin the selected specific encoding mode, and for outputting the codewordfor the encoding picture element to be encoded in the selected specificencoding mode.

The second encoding section may comprise:

a second predictor for calculating a prediction value of the encodingpicture element based on the value of the reference picture element;

a second prediction error calculator for calculating an error betweenthe value of the encoding picture element and the prediction valuecalculated by the second predictor as a prediction error; and

a third encoder for encoding the prediction error calculated by thesecond prediction error calculator for the encoding picture element tobe encoded in the selected encoding mode other than the specificencoding mode, regardless of whether the prediction error is thespecific value, and for outputting the codeword for the encoding pictureelement to be encoded in the selected encoding mode other than thespecific encoding mode.

The first encoder may comprise a first probability estimator forreceiving the result of the determination output from the determinatoras a sequence of binary symbols and estimating an occurrence probabilityof one of the binary symbols, and a first codeword allotter for encodingthe sequence of binary symbols, and

the second encoder may comprise a first error-to-symbol converter forreceiving the prediction error and converting the prediction error intoa sequence of binary symbols, a second probability estimator forreceiving the sequence of binary symbols and estimating an occurrenceprobability of one of the binary symbols, and a second codeword allotterfor encoding the sequence of binary symbols, and

the third encoder may comprise a second error-to-symbol converter forreceiving the prediction error and converting the prediction error intoa sequence of binary symbols, a third probability estimator forreceiving the sequence of binary symbols and estimating an occurrenceprobability of one of the binary symbols, and a third codeword allotterfor encoding the sequence of binary symbols.

The encoding controller may have a codeword transmission ordercontroller for changing an order for outputting codewords when acodeword has been determined by at least one of the first encoder, thesecond encoder, and the third encoder and when a codeword has not beendetermined by the other encoders.

In the encoding apparatus according to the present invention, at leastone of the first error-to-symbol converter and the seconderror-to-symbol converter successively may generate comparison valuesstarting with a value which would most likely occur as a predictionerror to be input to one of the first error-to-symbol converter and thesecond error-to-symbol converter, may successively compare the generatedvalues with the prediction error input to one of the firsterror-to-symbol converter and the second error-to-symbol converter oneby one, and may generate and output a sequence of binary symbols basedon a count of comparison time until one of the generated comparisonvalues coincides with the prediction error.

The mode determinator may select an encoding mode for an encodingpicture element based on an encoding mode for an encoded picture elementpreceding the encoding picture element.

In the encoding apparatus according to the present invention, at leastone of the first codeword allotter, the second codeword allotter, andthe third codeword allotter may change interpretation as to which one ofthe binary symbols is a more probable symbol, based on a change inprobability estimation for one of the binary symbols respectivelyimplemented by the first probability estimator for the first codewordallotter, the second probability estimator for the second codewordallotter, and the third probability estimator for the third codewordallotter.

The first predictor of the first encoding section and the secondpredictor of the second encoding section may be combined into apredictor.

At least two encoders of the first encoder, the second encoder, and thethird encoder may be combined into an encoder.

In the picture encoding apparatus according to the present invention,based on information as to which one of the binary symbols is a moreprobable symbol and an estimated occurrence probability of the moreprobable symbol, at least one of the first codeword allotter, the secondcodeword allotter, and the third codeword allotter may implementencoding for an enlarged information source of the binary symbolseffected by selecting a code most suited to a state of the enlargedinformation source of the binary symbols assumed from the estimatedoccurrence probability of the more probable symbol from a Huffman codeset prepared systematically for the enlarged information source of thebinary symbols.

A decoding apparatus according to the present invention may comprise:

a picture element memory for storing decoded picture elements havingvalues within a predetermined range, and outputting the value of one ofthe decoded picture elements adjacent to a decoding picture element as avalue of a reference picture element;

a mode determinator for selecting one of a specific decoding mode and adecoding mode other than the specific decoding mode from a plurality ofpredefined decoding modes for the decoding picture element based on thevalue of the reference picture element;

a first decoding section for receiving a codeword, predicting a value ofthe decoding picture element, determining whether the prediction iscorrect, and for decoding the codeword into the value of the decodingpicture element based on a result of the determination;

a second decoding section for receiving a codeword for the decodingpicture element, predicting the value of the decoding picture element,decoding the codeword into the value of the decoding picture elementwithout determining whether the prediction is correct; and

a decoding controller for selectively operating the first decodingsection and the second decoding section based on one of the specificdecoding mode and the decoding mode other than the specific decodingmode selected by the mode determinator.

The first decoding section may comprise:

a first predictor for calculating a prediction value of the decodingpicture element based on the value of the reference picture element;

a first decoder for decoding the codeword for the decoding pictureelement to be decoded in the selected specific decoding mode into aresult of determination indicating whether a prediction error ispredetermined value;

a second decoder for decoding the codeword for the decoding pictureelement to be decoded in the selected specific decoding mode and havingthe prediction error other than the predetermined value into theprediction error other than the predetermined value;

a first decoding picture element calculator for calculating the value ofthe decoding picture element based on the prediction value of thedecoding picture element calculated by the first predictor, the resultof the determination, and the prediction error obtained by the seconddecoder.

The second decoding section may comprise:

a second predictor for calculating a prediction value of the decodingpicture element based on the value of the reference picture element;

a third decoder for decoding the codeword for the decoding pictureelement to be decoded in the selected decoding mode other than thespecific decoding mode into the prediction error regardless of whetherthe prediction error is the predetermined value;

a second decoding picture element calculator for calculating the valueof the decoding picture element to be decoded in the selected decodingmode other than the specific decoding mode based on the prediction valueof the decoding picture element calculated by the second predictor andthe prediction error obtained by the third decoder.

The first decoder may have a first symbol restoring device for receivingthe codeword and decoding the codeword into a sequence of binary symbolsand a first probability estimator for estimating an occurrenceprobability of one of the binary symbols, and wherein the first decoderoutputs one of the binary symbols as a result of determination, and

the second decoder may have a second symbol restoring device forreceiving the codeword and decoding the codeword into a sequence ofbinary symbols, a second probability estimator for receiving the binarysymbols and estimating an occurrence probability of one of the binarysymbols, and a first symbol-to-error converter for receiving thesequence of binary symbols and converting the sequence of binary symbolsinto the prediction error, and

the third decoder may have a third symbol restoring device for receivingthe codeword and decoding the codeword into a sequence of binarysymbols, a third probability estimator for receiving the binary symbolsand estimating an occurrence probability of one of the binary symbols,and a second symbol-to-error converter for receiving the sequence ofbinary symbols and converting the sequence of binary symbols into theprediction error.

The decoding controller may have a binary-symbol sequence using ordercontroller for changing an order of using decoded binary symbols in acase where, before all sequences of binary symbols decoded by at leastone of the first decoder, the second decoder, and the third decoder areused up, a sequence of binary symbols is output from the other one ofthe first decoder, the second decoder, and the third decoder.

In the decoding apparatus according to the present invention, at leastone of the first symbol-to-error converter and the secondsymbol-to-error converter may convert the input sequence of binarysymbols into the prediction error based on a value and a number of thebinary symbols input.

The mode determinator may select a decoding mode for a decoding pictureelement based on a decoding mode for a decoded picture element precedingthe decoding picture element.

In the decoding apparatus according to the present invention, at leastone of the first symbol restoring device, the second symbol restoringdevice, and the third symbol restoring device may change interpretationas to which one of the binary symbols is a more probable symbol based ona change in probability estimation for the binary symbols respectivelyimplemented by the first probability estimator for the first symbolrestoring device, the second probability estimator for the second symbolrestoring device and the third probability estimator for the thirdsymbol restoring device.

The first predictor of the first decoding section and the secondpredictor of the second decoding section may be combined into apredictor.

At least two decoders of the first decoder, the second decoder, and thethird decoder may be combined into a decoder.

In the decoding apparatus according to the present invention, based oninformation as to which one of the binary symbols is a more probablesymbol and an estimated occurrence probability of the more probablesymbol, at least one of the first symbol restoring device, the secondsymbol restoring device, and the third symbol restoring device mayimplement decoding for an enlarged information source of binary symbolseffected by selecting a code most suited to a state of the enlargedinformation source of binary symbols assumed from the estimatedoccurrence probability of the more probable symbol from a Huffman codeset prepared systematically for the enlarged information source ofbinary symbols.

An encoding method according to the present invention may comprise:

an outputting step of receiving and storing a picture element having avalue within a predetermined range as an encoding picture element,outputting the value of the encoding picture element, and outputting avalue of an encoded picture element adjacent to the encoding pictureelement as the value of a reference picture element;

a mode deciding step of selecting one of a specific encoding mode and anencoding mode other than the specific encoding mode from predefinedencoding modes for the encoding picture element based on the value ofthe reference picture element;

a first main encoding step of predicting the value of the encodingpicture element, determining whether the prediction is correct, encodingthe value of the encoding picture element based on a result ofdetermination, and outputting a codeword for the encoding pictureelement;

a second main encoding step of predicting the value of the encodingpicture element, encoding the value of the encoding picture elementwithout determining whether the prediction is correct, and outputting acodeword for the encoding picture element; and

an encoding controlling step of selectively operating the first mainencoding step and the second main encoding step based on the specificencoding mode and the encoding mode other than the specific encodingmode selected by the mode deciding step.

The first main encoding step may comprise:

a first predicting step of calculating a prediction value of theencoding picture element based on the value of the reference pictureelement;

a first prediction error calculating step of calculating an errorbetween the value of the encoding picture element and the predictionvalue calculated by the first predicting step as a prediction error;

a determination step of determinating whether the prediction errorcalculated by the first prediction error calculating step is apredetermined value, and outputting a result of the determination;

a first encoding step of receiving and encoding the result of thedetermination output by the determination step and outputting thecodeword for the encoding picture element to be encoded in the selectedspecific encoding mode; and

a second encoding step of encoding the prediction error calculated bythe first prediction error calculating step when the prediction error isother than the predetermined value for the encoding picture element tobe encoded in the selected specific encoding mode, and outputting thecodeword for the encoding picture element to be encoded in the selectedspecific encoding mode.

The second main encoding step may comprise:

a second predicting step of calculating a prediction value of theencoding picture element based on the value of the reference pictureelement;

a second prediction error calculating step of calculating an errorbetween the value of the encoding picture element and the predictionvalue calculated by the second predicting step as a prediction error;and

a third encoding step of encoding the prediction error calculated by thesecond prediction error calculating step for the encoding pictureelement to be encoded in the selected encoding mode other than thespecific encoding mode, regardless of whether the prediction error isthe predetermined value, and outputting the codeword for the encodingpicture element to be encoded in the selected encoding mode other thanthe specific encoding mode.

The first encoding step may comprise a first probability estimating stepof receiving the result of the determination output by the determinationstep as a sequence of binary symbols and estimating an occurrenceprobability of one of the binary symbols and a first codeword allottingstep of encoding the sequence of binary symbols,

the second encoding step may comprise a first error-to-symbol convertingstep of receiving the prediction error and converting the predictionerror into a sequence of binary symbols, a second probability estimatingstep of receiving the sequence of binary symbols and estimating anoccurrence probability of one of the binary symbols, and a secondcodeword allotting step of encoding the sequence of binary symbols, and

the third encoding step may comprise a second error-to-symbol convertingstep of receiving the prediction error and converting the predictionerror into a sequence of binary symbols, a third probability estimatingstep of receiving the sequence of binary symbols and estimating anoccurrence probability of one of the binary symbols, and a thirdcodeword allotting step of encoding the sequence of binary symbols.

In the encoding method according to the present invention, at least oneof the first codeword allotting step, the second codeword allottingstep, and the third codeword allotting step may include a step ofchanging interpretation as to which one of the binary symbols is a moreprobable symbol based on a change in probability estimation for thebinary symbols respectively implemented by the first probabilityestimating step for the first codeword allotting step, the secondprobability estimating step for the second codeword allotting step, andthe third probability estimating step for the third codeword allottingstep.

In the encoding method according to the present invention, based oninformation as to which one of the binary symbols is a more probablesymbol and an estimated occurrence probability of the more probablesymbol, at least one of the first codeword allotting step, the secondcodeword allotting step, and the third codeword allotting step mayimplement encoding for an enlarged information source of the binarysymbols effected by selecting a code most suited to a state of theenlarged information source of the binary symbols assumed from theestimated occurrence probability of the more probable symbol from aHuffman code set prepared systematically for the enlarged informationsource of the binary symbols.

A decoding method according to the present invention may comprise:

an outputting step of storing decoded picture elements having valueswithin a predetermined range, and outputting the value of one of thedecoded picture elements adjacent to a decoding picture element as thevalue of a reference picture element:

a mode deciding step of selecting one of a specific decoding mode and adecoding mode other than the specific decoding mode from a plurality ofpredefined decoding modes for the decoding picture element based on thevalue of the reference picture element;

a first main decoding step of receiving a codeword, predicting a valueof the decoding picture element, determining whether the prediction iscorrect, and decoding the codeword into the value of the decodingpicture element based on a result of the determination;

a second main decoding step of receiving a codeword, predicting thevalue of the decoding picture element, and decoding the codeword intothe value of the decoding picture element without determining whetherthe prediction is correct; and

a decoding controlling step of selectively operating the first maindecoding step and the second main decoding step based on the specificdecoding mode and the decoding mode other than the specific decodingmode selected by the mode deciding step.

The first main decoding step may comprise:

a first predicting step of calculating a prediction value of thedecoding picture element based on the value of the reference pictureelement;

a first decoding step of decoding the codeword for the decoding pictureelement to be decoded in the selected specific decoding mode into aresult of determination indicating whether a prediction error is apredetermined value;

a second decoding step of decoding the codeword for the decoding pictureelement to be decoded in the selected specific decoding mode and havingthe prediction error other than the predetermined value into theprediction error other than the predetermined value; and

a first decoding picture element calculating step of calculating thevalue of the decoding picture element based on the prediction value forthe decoding picture element calculated by the first predicting step,the result of the determination, and the prediction error other than thepredetermined value obtained by the second decoding step.

The second main decoding step may comprise:

is a second predicting step of calculating a prediction value of thedecoding picture element based on the value of the reference pictureelement;

a third decoding step of decoding the codeword for the decoding pictureelement to be decoded in the selected decoding mode other than thespecific decoding mode into a prediction error regardless of whether theprediction error is the predetermined value; and

a second decoding picture element calculating step of calculating thevalue of the decoding picture element to be decoded in the selecteddecoding mode other than the specific decoding mode based on theprediction value calculated by the second predicting step and theprediction error calculated by the third decoding step.

The first decoding step may comprise a first symbol restoring step forreceiving the codeword and decoding the codeword into a sequence ofbinary symbols and a first probability estimating step of estimating anoccurrence probability of one of the binary symbols, and a step ofoutputting one of the binary symbols as a result of the determination,

the second decoding step may comprise a second symbol restoring step ofreceiving the codeword and decoding the codeword into a sequence ofbinary symbols, a second probability estimating step of estimating anoccurrence probability of one of the binary symbols, and a firstsymbol-to-error converting step of receiving the sequence of binarysymbols and converting the sequence of binary symbols into theprediction error, and

the third decoding step may comprise a third symbol restoring step ofreceiving the codeword and decoding the codeword into a sequence ofbinary symbols, a third probability estimating step of receiving thebinary symbols and estimating an occurrence probability of one of thebinary symbols, and a second symbol-to-error converting step ofreceiving the sequence of binary symbols and converting the sequence ofbinary symbols into the prediction error.

In the decoding method according to the present invention, at least oneof the first symbol restoring step, the second symbol restoring step,and the third symbol restoring step may include a step of changinginterpretation as to which one of the binary symbols is a more probablesymbol based on a change in probability estimation for the binarysymbols respectively implemented by the first probability estimatingstep for the first symbol restoring step, the second probabilityestimating step for the second symbol restoring step, and the thirdprobability estimating step for the third symbol restoring step.

In the decoding method according to the present invention, based oninformation as to which one of the binary symbols is a more probablesymbol and an estimated occurrence probability of the more probablesymbol, at least one of the first symbol restoring step, the secondsymbol restoring step, and the third symbol restoring step may implementdecoding for an enlarged information source of binary symbols effectedby selecting a code most suited to a state of the enlarged informationsource of binary symbols assumed from the estimated occurrenceprobability of the more probable symbol from a Huffman code set preparedsystematically for the enlarged information source of binary symbols.

The encoding apparatus may be provided in a semiconductor chip.

The encoding apparatus may be provided in a circuit board.

A picture encoding apparatus according to the present invention forreceiving picture signals representing picture elements, encoding thepicture elements represented by the picture signals into codes by usingan encoding apparatus therein, and for outputting the codes to asubsequent processing apparatus, the encoding apparatus may comprise:

a picture element memory for receiving and storing a picture elementhaving a value within a predetermined range as an encoding pictureelement, outputting the value of the encoding picture element, and foroutputting a value of an encoded picture element adjacent to theencoding picture element as the value of a reference picture element;

a mode determinator for selecting one of a specific encoding mode and anencoding mode other than the specific encoding mode from a plurality ofpredefined encoding modes for the encoding picture element based on thevalue of the reference picture element;

a first encoding section for predicting the value of the encodingpicture element, determining whether the prediction is correct, encodingthe value of the encoding picture element based on a result of thedetermination, and for outputting a codeword for the encoding pictureelement;

a second encoding section for predicting the value of the encodingpicture element, encoding the value of the encoding picture elementwithout determining whether the prediction is correct, and foroutputting a codeword for the encoding picture element; and

an encoding controller for selectively operating the first encodingsection and the second encoding section based on one of the specificencoding mode and the encoding mode other than the specific encodingmode selected by the mode determinator.

The picture processing apparatus may be an electronic computer.

The picture processing apparatus may be a scanner.

The picture processing apparatus may be a facsimile machine.

The picture processing apparatus may be a display unit.

The picture processing apparatus may be a storage device.

The decoding apparatus may be provided in a semiconductor chip.

The decoding apparatus may be provided in a circuit board.

A picture processing apparatus according to the present invention forreceiving a picture signal representing a code for a picture element,decoding the code into the value of the picture element by a decodingapparatus therein, and for outputting the picture element to asubsequent processing apparatus, the decoding apparatus may comprise:

a picture element memory for storing decoded picture elements havingvalues within a predetermined range and outputting the value of one ofthe decoded picture elements adjacent to a decoding picture element asthe value of a reference picture element;

a mode determinator for selecting one of a specific decoding mode and adecoding mode other than the specific decoding mode from a plurality ofpredefined decoding modes for the decoding picture element based on thevalue of the reference picture element;

a first decoding section for receiving a codeword, predicting a value ofthe decoding picture element, determining whether the prediction iscorrect, and for decoding the codeword into the value of the decodingpicture element based on a result of the determination;

a second decoding section for receiving a codeword, predicting the valueof the decoding picture element, and for decoding the codeword into thevalue of the decoding picture element without determining whether theprediction is correct; and

a decoding controller for selectively operating the first decodingsection and the second decoding section based on the result of thedetermination made by the specific decoding mode and the decoding modeother than the specific decoding mode selected by the mode determinator.

The picture processing apparatus may be an electronic computer.

The picture processing apparatus may be a scanner.

The picture processing apparatus may be a facsimile machine.

The picture processing apparatus may be a printer.

The picture processing apparatus may be a display unit.

The picture processing apparatus may be a storage device.

The encoding apparatus according to the present invention may comprise:

a picture element memory for receiving and storing a picture elementhaving a value within a predetermined range as an encoding pictureelement, outputting the value of the encoding picture element, and foroutputting a value of an encoded picture element adjacent to theencoding picture element as the value of a reference picture element;

an encoding section for predicting the value of the encoding pictureelement, determining whether the prediction is correct, encoding thevalue of the encoding picture element based on a result of thedetermination, and for outputting a codeword for the encoding pictureelement; and

an encoding controller for operating the encoding section based on theresult of the prediction made by the encoding section.

The encoding section may comprise:

a predictor for calculating a prediction value of the encoding pictureelement based on the value of the reference picture element;

a prediction error calculator for calculating an error between the valueof the encoding picture element and the prediction value calculated bythe predictor (3) as a prediction error;

a determinator for determining whether the prediction error calculatedby the prediction error calculator is a specific value and foroutputting a result of determination;

a first encoder for receiving the result of determination output fromthe determinator, encoding the result of determination, and foroutputting the codeword; and

a second encoder for encoding the prediction error calculated by theprediction error calculator when the prediction error is other than thespecific value for the encoding picture element to be encoded and foroutputting the codeword for the encoding picture element to be encoded.

A decoding apparatus according to the present invention may comprise:

a picture element memory for storing decoded picture elements havingvalues within a predetermined range and for outputting the value of oneof the decoded picture elements adjacent to a decoding picture elementas the value of a reference picture element;

a decoding section for receiving a codeword, predicting a value of thedecoding picture element, determining whether the prediction is correct,and for decoding the codeword into the value of the decoding pictureelement based on a result of the determination; and

a decoding controller for operating the decoding section based on theresult of the determination made by the decoding section.

The decoding section may comprise:

a predictor for calculating a prediction value for the decoding pictureelement based on the value of the reference picture element;

a first decoder for decoding the codeword into a result of determinationwhether a prediction error is a predetermined value;

a second decoder for decoding the codeword for the decoding pictureelement whose prediction error is not the predetermined value into theprediction error;

a decoding picture element calculator for calculating the value of thedecoding picture element based on the prediction value calculated by thepredictor, the result of the determination, and the prediction errorobtained by the second decoder.

A picture processing apparatus according to the present invention maycomprise:

a picture pick-up device for picking up a picture composed of aplurality of picture elements;

a picture compression circuit for compressing the picked-up picture; and

a memory for storing the compressed picture, and

the picture compression circuit may comprise an encoding apparatuscomprising:

a picture element memory for receiving and storing a picture elementhaving a value within a predetermined range as an encoding pictureelement, outputting the value of the encoding picture element, and foroutputting a value of an encoded picture element adjacent to theencoding picture element as the value of a reference picture element;

a mode determinator for selecting one of a specific encoding mode and anencoding mode other than the specific encoding mode from a plurality ofpredefined encoding modes for the encoding picture element based on thevalue of the reference picture element;

a first encoding section for predicting the value of the encodingpicture element, determining whether the prediction is correct, encodingthe value of the encoding picture element based on a result of thedetermination, and for outputting a codeword for the encoding pictureelement;

a second encoding section for predicting the value of the encodingpicture element, encoding the value of the encoding picture elementwithout determining whether the prediction is correct, and foroutputting a codeword for the encoding picture element; and

an encoding controller for selectively operating the first encodingsection and the second encoding section based on one of the specificencoding mode and the encoding mode other than the specific encodingmode selected by the mode determinator.

A picture processing apparatus according to the present invention maycomprise:

a picture pick-up device for picking up a picture composed of aplurality of picture elements;

a picture compression circuit for compressing the picked-up picture;

a memory for storing the compressed picture; and

a picture expansion circuit for expanding the stored picture, and

the picture expansion circuit may comprise a decoding apparatuscomprising:

a picture element memory for storing decoded picture elements havingvalues within a predetermined range, and outputting the value of one ofthe decoded picture elements adjacent to a decoding picture element as avalue of a reference picture element;

a mode determinator for selecting one of a specific decoding mode and adecoding mode other than the specific decoding mode from a plurality ofpredefined decoding modes for the decoding picture element based on thevalue of the reference picture element;

a first decoding section for receiving a codeword, predicting a value ofthe decoding picture element, determining whether the prediction iscorrect, and for decoding the codeword into the value of the decodingpicture element based on a result of the determination;

a second decoding section for receiving a codeword for the decodingpicture element, predicting the value of the decoding picture element,decoding the codeword into the value of the decoding picture elementwithout determining whether the prediction is correct; and

a decoding controller for selectively operating the first decodingsection and the second decoding section based on one of the specificdecoding mode and the decoding mode other than the specific decodingmode selected by the mode determinator.

The picture compression circuit may comprise a plurality of the encodingapparatuses for inputting a luminance signal Y and color-differencesignals U, V in parallel and for encoding the signals.

The picture compression circuit may comprise a plurality of the encodingapparatuses for inputting color signals R, G, B in parallel and forencoding the signals.

The picture compression circuit may comprise one encoding apparatus forserially inputting a luminance signal Y and color-difference signals U,V by a block unit and for encoding the signals.

The picture compression circuit may comprise one encoding apparatus forserially inputting color signals R, G, B by a block unit and forencoding the signals.

The picture expansion circuit may comprise a plurality of the decodingapparatuses for inputting an encoded luminance signal Y and encodedcolor-difference signals U, V in parallel and for decoding the signals.

The picture expansion circuit may comprise a plurality of the decodingapparatuses for inputting encoded color signals R, G, B in parallel andfor decoding the signals.

The picture expansion circuit may comprise one decoding apparatus forserially inputting an encoded luminance signal Y and encodedcolor-difference signals U, V by a block unit and for decoding thesignals.

The picture expansion circuit may comprise one decoding apparatus forserially inputting encoded color signals R, G, B by a block unit and fordecoding the signals.

Further scope of applicability of the present invention will becomeapparent from the detailed description given hereinafter. However, itshould be understood that the detailed description and specificexamples, while indicating preferred embodiments of the invention, aregiven by way of illustration only, since various changes andmodifications within the spirit and scope of the invention will becomeapparent to those skilled in the art from this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will becomes more fully understood from thedetailed description given hereinbelow and the accompanying drawingswhich are given by way of illustration only, and thus are not limitativeof the present invention, and wherein:

FIG. 1 is a perspective view showing a picture processing apparatusaccording to the present invention.

FIG. 2 is a perspective view showing an application of a pictureprocessing apparatus according to the present invention.

FIG. 3 is a table showing the states in which binary symbols to beencoded belong and the code orders.

FIG. 4 is a block diagram showing a configuration of an encodingapparatus according to the first embodiment.

FIG. 5 is a block diagram showing a configuration of a first encoderaccording to the present invention.

FIG. 6 is a block diagram showing a configuration of a second encoderaccording to the present invention.

FIG. 7 is a block diagram showing a configuration of a third encoderaccording to the present invention.

FIG. 8 is a table showing examples of conversion of prediction errorsinto binary symbols performed by the second encoder.

FIG. 9 is a table showing examples of conversion of prediction errorsinto binary symbols performed by the third encoder.

FIG. 10 is a flow chart showing a flow of an encoding process accordingto the present invention.

FIG. 11 is a diagram showing examples of encoding conditions forencoding picture elements according to the present invention.

FIG. 12 is a diagram showing an encoding operation according to thepresent invention.

FIG. 13 is a block diagram showing a configuration of a decodingapparatus according to the first embodiment.

FIG. 14 is a block diagram showing a configuration of a first decoderaccording to the present invention.

FIG. 15 is a block diagram showing a configuration of a second decoderaccording to the present invention.

FIG. 16 is a block diagram showing a configuration of a third decoderaccording to the present invention.

FIG. 17 is a block diagram showing a configuration of an encodingapparatus according to the second embodiment of the present invention.

FIG. 18 is a flow chart showing a flow of an encoding process accordingto the present invention.

FIG. 19 is a diagram showing an encoding operation according to thepresent invention.

FIG. 20 is a flow chart showing a flow of the control processimplemented by the encoding controller after a codeword has beendetermined by the third encoder.

FIG. 21 is a flow chart showing a flow of the control processimplemented by the encoding controller after a codeword has beendetermined by the first encoder.

FIG. 22 is a flow chart showing a flow of the control processimplemented by the encoding controller after a codeword has beendetermined by the first encoder because of the occurrence of an LPS in abinary symbol sequence.

FIG. 23 is a diagram showing an encoding operation according to thepresent invention.

FIG. 24 is a flow chart showing a flow of a picture-element prefetchoperation according to the present invention.

FIG. 25 is a block diagram showing a configuration of a decodingapparatus according to the second embodiment of the present invention.

FIG. 26 is a block diagram showing a configuration of an encodingapparatus according to the third embodiment of the present invention.

FIG. 27 is a block diagram showing a configuration of an encoder Saaccording to the third embodiment of the present invention.

FIG. 28 is a block diagram showing a configuration of an encoder 6 aaccording to the third embodiment of the present invention.

FIG. 29 is a block diagram showing a configuration of an encoder 8 aaccording to the third embodiment of the present invention.

FIG. 30 is a flow chart showing a flow of an operation implemented by aprobability estimator and a truth table according to the thirdembodiment of the present invention.

FIG. 31 is a diagram showing how encoding is implemented according tothe present invention when the interpretation of the MPS and the LPS hasbeen changed.

FIG. 32 is a block diagram showing a configuration of a decodingapparatus according to the third embodiment of the present invention.

FIG. 33 is a block diagram showing a configuration of a decoder 45 aaccording to the third embodiment of the present invention.

FIG. 34 is a block diagram showing a configuration of a decoder 46 aaccording to the third embodiment of the present invention.

FIG. 35 is a block diagram showing a configuration of a decoder 48 aaccording to the third embodiment of the present invention.

FIG. 36 is a block diagram showing a configuration of an encodingapparatus according to the fourth embodiment of the present invention.

FIG. 37 is a block diagram showing a configuration of a decodingapparatus according to the fourth embodiment of the present invention.

FIG. 38 is a diagram showing a case where a plurality of MPS countersare present inside an encoder according to the present invention.

FIG. 39 is a block diagram showing a configuration of an encodingapparatus according to the fifth embodiment of the present invention.

FIG. 40 is a block diagram showing a configuration of a decodingapparatus for the encoding apparatus illustrated in FIG. 39.

FIG. 41 is a block diagram showing another configuration of an encodingapparatus according to the fifth embodiment of the present invention.

FIG. 42 is a block diagram showing a configuration of an encoder 5 billustrated in FIG. 41.

FIG. 43 is a block diagram showing a configuration of a decodingapparatus for the encoding apparatus illustrated in FIG. 41.

FIG. 44 is a block diagram showing a configuration of a decoder 45 bused in the decoding apparatus illustrated in FIG. 43.

FIG. 45 is a block diagram showing another configuration of an encodingapparatus according to the fifth embodiment of the present invention.

FIG. 46 is a block diagram showing an encoder 6 b used in the encodingapparatus illustrated in FIG. 45.

FIG. 47 is a block diagram showing a configuration of a decodingapparatus for the encoding apparatus illustrated in FIG. 45.

FIG. 48 is a block diagram showing a configuration of a decoder 46 bused in the decoding apparatus illustrated in FIG. 47.

FIG. 49 is a block diagram showing another configuration of an encodingapparatus according to the fifth embodiment of the present invention.

FIG. 50 is a block diagram showing a configuration of an encoder 5 cused in the encoding apparatus illustrated in FIG. 49.

FIG. 51 is a block diagram showing a configuration of an encodingapparatus according to the sixth embodiment of the present invention.

FIG. 52 is a block diagram showing a configuration of a decodingapparatus according to the sixth embodiment of the present invention.

FIG. 53 shows an example of a configuration of a picture processingapparatus according to the seventh embodiment of the present invention.

FIG. 54 shows a sequence of writing procedure of a static picture by thepicture processing apparatus according to the seventh embodiment of thepresent invention.

FIG. 55 shows a configuration of a picture compression circuit 318 ofthe invention.

FIG. 56 shows a configuration of a picture expansion circuit 320 of theinvention.

FIG. 57 shows another configuration of the picture compression circuit318 of the invention.

FIG. 58 shows another configuration of the picture expansion circuit 320of the invention.

FIG. 59 shows another configuration of the picture processing apparatusof the invention.

FIG. 60 shows another configuration of the picture processing apparatusof the invention.

FIG. 61 shows the picture processing apparatus of the invention and thecomputer 700.

FIG. 62 shows another configuration of the picture compression circuit318 of the invention.

FIG. 63 shows another configuration of the picture compression circuit318 of the invention.

FIG. 64 shows another configuration of the picture compression circuit318 of the invention.

FIG. 65 shows another configuration of the picture compression circuit318 of the invention.

FIG. 66 is a block diagram showing a configuration of a conventionalencoding apparatus.

FIG. 67 are tables showing a conventional encoding and decoding method.

FIG. 68 is a table showing a conventional state transition method ofdetermining the code order.

FIG. 69 is a diagram showing an encoding or decoding picture element andreference picture elements.

FIG. 70 shows a configuration of a conventional picture compressioncircuit and a conventional picture expansion circuit.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1

FIG. 1 is a perspective view showing a configuration of a pictureprocessing apparatus having an encoder according to the presentinvention.

A picture processing apparatus having a decoder according to the presentinvention also has the configuration similar to that of the pictureprocessing apparatus illustrated in FIG. 1.

In FIG. 1, a picture processing apparatus 60 includes a display unit 61,a keyboard 62, a mouse 63, a mouse pad 64, a system unit 65, and acompact disc drive 100.

As shown in FIG. 1, for example, a picture processing apparatus having adecoder according to the present invention receives encoded pictureinformation from the compact disc drive 100, decodes the encoded pictureinformation, transfers the decoded picture information to the systemunit 65, and displays the decoded picture information on the displayunit 61. A picture processing apparatus according to the presentinvention encodes picture information displayed on the display unit 61and supplies the encoded picture information to the compact disc drive100. Alternatively, a picture processing apparatus according to thepresent invention encodes picture information and transmits the encodedpicture information via a transmission line (not shown). Theconfiguration of the picture processing apparatus according to thepresent invention does not have to be limited to the configuration of apersonal computer or a workstation as shown in FIG. 1. Other types ofconfigurations using other components may also be used. A video player,for example, may be used as an input device instead of the compact discdrive 100, or picture data from a network may be input in place of thepicture information. The input data may be either in analog format or indigital format.

A picture processing apparatus according to the present invention may beprovided as an independent apparatus, as shown in FIG. 1. However, itmay be housed inside the housing of a peripheral device such as aprinter 66, a scanner 68, a facsimile machine 69, a display apparatus(such as the display unit 61), or a storage device (such as the compactdisc drive 100), as shown in FIG. 2. That is, a picture processingapparatus according to the present invention is defined herein to be anelectronic apparatus having an encoding apparatus or a decodingapparatus which will be hereinafter described. Or, a picture processingapparatus according to the present invention is also defined to be anelectronic apparatus for implementing an encoding method or a decodingmethod which will be hereinafter described.

An encoding apparatus or a decoding apparatus according to the presentinvention may be provided as an independent apparatus. Alternatively, itmay be incorporated into a system board of a television camera, ameasuring device, or a computer, or it may be incorporated as a part ofa circuit board, or it may be provided in a semiconductor chip. It maybe implemented in a type of a communication system by connectingindividual devices illustrated in FIG. 2 via a local area network (notshown in FIG. 2) to transmit encoded information therebetween.Alternatively, it may be implemented in a type of a communication systemfor receiving and transmitting encoded information via a wide areanetwork such as the ISDN (Integrated Services Digital Network).

In this embodiment, the encoding or the decoding method described inFIG. 67 is assumed to be applied to an encoder in an encoding apparatusor a decoder in a decoding apparatus according to the present invention.In this embodiment, it is assumed that encoding or 1S decoding for anextended information source of binary symbols (a binary symbol sequence)is implemented, based on the information which one of the binary symbolsis MPS and based on the estimated occurrence probability of the MPS, byselecting codeword tables from a set of Huffman codeword tables preparedsystematically for the extended information source of binary symbols (abinary symbol sequence) as shown in FIG. 67. The code can be most suitedto the state of the extended information source of binary symbolsdecided from the estimated occurrence probability of the MPS. It is alsoassumed that, as shown in FIG. 3, code orders are set respectively forthe thirty-two states. Based on the state transition rule as shown inFIG. 3, a plurality of encoders or decoders, which will be hereinafterdescribed, respectively and independently set one of the thirty-twostates and one of the corresponding code orders and encode or decodebinary symbols.

A configuration and an operation of an encoding apparatus according tothe first embodiment of the present invention will be describedexplaining the switching between encoding modes and the conversion of aprediction error between the value of an encoding picture element and aprediction value therefor into a binary symbol sequence.

FIG. 4 shows a configuration of an encoding apparatus 400 according tothe first embodiment of the present invention.

First, the configured elements of the encoding apparatus 400 accordingto this embodiment will be described.

In FIG. 4, reference numeral 1 indicates a picture element memory forreceiving, storing, and outputting the value of an encoding pictureelement. The picture element memory 1 also outputs the value of at leastone encoded picture element which has been already stored in the pictureelement memory 1 and which is adjacent to the encoding picture elementas a reference picture element.

Reference numeral 2 indicates a mode determinator for deciding the modeA or the mode B, based on the value of the at least one referencepicture element and for outputting a mode discrimination signal CM. Amode decision method for deciding the mode A or the mode B will behereinafter described.

Reference numeral 3 indicates a first predictor for calculating in themode A the prediction value of the encoding picture element by referringto the value(s) of the reference picture element(s).

Reference numeral 30 represents a first prediction error calculator forsubtracting the prediction value calculated by the predictor 3 from thevalue of the encoding picture element and for determining the predictionerror.

Reference numeral 4 indicates a zero determinator for converting theprediction error between the value of the encoding picture element andthe prediction value calculated by the predictor 3 into a binary symbolindicating whether the prediction error is 0 or not 0. Then, the zerodeterminator 4 outputs the converted binary symbol. In this embodimentand the embodiments which will be hereinafter described, a zerodeterminator is provided for determining whether a prediction error iszero or not. However, this determinator may be a determinator fordetermining whether or not a prediction error is a predetermined valuesuch as, for example, one or not one, or −3 or not −3, and the like.

Reference numeral 5 indicates a first encoder for encoding in the mode Athe binary symbol which has been output from the zero determinator 4.

Reference numeral 6 indicates a second encoder for encoding a predictionerror in the mode A except when the prediction error is zero. (When theabove-mentioned determinator determines whether a prediction error isone or not one, the second encoder 6 encodes a prediction error in themode A except when the prediction error is one. Similarly, when theabove-mentioned determinator determines whether a prediction error is −3or not −3, the second encoder 6 encodes a prediction error in the mode Aexcept when the prediction error is −3.)

Reference numeral 7 indicates a second predictor for calculating in themode B the prediction value of an encoding picture element by referringto the value(s) of the reference picture element(s).

Reference numeral 31 indicates a second prediction error calculator fordetermining the prediction error by subtracting the prediction valuecalculated by the predictor 7 from the value of the encoding pictureelement.

Reference numeral 8 represents a third encoder for encoding in the modeB the prediction error between the value of the encoding picture elementand the prediction value calculated by the predictor 7.

Reference numeral 9 represents a code switching device for selecting andoutputting an appropriate codeword among the codewords supplied from thefirst encoder 5, the second encoder 6, and the third encoder 8.

Reference numeral 10 represents a code buffer for receiving codewordsselected by the code switching device 9 and for outputting a sequence ofcodes in the order the codewords have been supplied to the code buffer.

Reference numeral 11 indicates an encoding controller for controllingthe picture element memory 1, the first encoder 5, the second encoder 6,and the third encoder 8, the code switching device 9, and the codebuffer 10, based on the mode discrimination signal CM and controlsignals C1 through C6.

Reference numeral 101 indicates a first encoding section provided withthe first encoder 5 which encodes in the mode A a binary symbolindicating whether or not a prediction error between the value of anencoding picture element and the estimated prediction value is zero, andthe second encoder 6 which encodes a prediction error in the mode A whenthe prediction error is not zero.

Reference numeral 102 indicates a second encoding section 102 providedwith the third encoder 8 which encodes in the mode B a prediction errorregardless of whether or not the prediction error between the value ofan encoding picture element and the estimated prediction value is zero.

FIGS. 5 through 7 are block diagrams showing internal configurations ofthe first encoder 5, the second encoder 6, and the third encoder 8respectively.

Referring to FIGS. 5 through 7, the first encoder 5, the second encoder6, and the third encoder 8 include the first probability estimator 25,the second probability estimator 26, and the third probability estimator28 respectively for receiving a sequence of binary symbols andestimating the occurrence probability of the More Probable Symbols (MPS)for the binary symbols. Furthermore, the first encoder 5, the secondencoder 6, and the third encoder 8 have a first codeword allotter 15, asecond codeword allotter 16, and a third codeword allotter 18respectively for receiving a sequence of binary symbols and theestimated occurrence probability of the MPS estimated by the probabilityestimators, for encoding the sequence of binary symbols, and foroutputting codewords. The first probability estimator 25, the secondprobability estimator 26, and the third probability estimator 28determine the code orders shown in FIG. 3, and supply the code orders tothe first codeword allotter 15, the second codeword allotter 16, and thethird codeword allotter 18 respectively. In other words, the probabilityestimator changes the code order to an appropriate value based on theoccurrence probability of the MPS estimated from past data on binarysymbol sequences. For this reason, an encoding efficiency can beenhanced.

There are possibly two methods by which probability estimators determinethe code order. Both of the two methods have already been describedhereinbefore as the conventional related arts.

The first example of the two methods is the state transition method. Inthis system, the state number assigned to specify each of the thirty-twostates shown in FIG. 3 is increased by one when the number of MPSsconsecutively occurred has become equal to the code order. On the otherhand, when an LPS has occurred before the number of MPSs consecutivelyoccurred becomes equal to the code order, the state number is decreasedby one.

The second example of the two methods is to count the number of binarysymbols “0” and binary symbols “1” which have occurred in a binarysymbol sequence and which are respectively indicated by N(0) and N(1),and determine the code order based on the result of the count.

The probability estimator may estimate the occurrence probability of theMPS by using a method other than the abovementioned first code orderdetermination method or the second code order determination method.

Referring to FIG. 6 and FIG. 7, the second encoder 6 and the thirdencoder 8 have the first error-to-symbol converter 36 and the seconderror-to-symbol converter 38 respectively for converting a predictionerror to binary symbol(s). The error-to-symbol converter 36 performsconversion as shown in FIG. 8. On the other hand, the error-to-symbolconverter 38 performs conversion as shown in FIG. 9. The conversionperformed by the error-to-symbol converter 36 or the error-to-symbolconverter 38 can be effected by prestoring the tables as shown in FIG. 8and FIG. 9 and then converting a prediction error into binary symbol(s),by retrieving the tables. Alternatively, a correspondence between theprediction error and binary symbol(s) shown in FIG. 8 and FIG. 9 may beachieved by using an algorithm which will be described hereinafter. Thealgorithm involves the step of generating comparison valuessuccessively, starting with the value which would most likely occur as aprediction error to be supplied to the error-to-symbol converter 36 orthe error-to-symbol converter 38, that is, in order from the lowestabsolute value of the prediction error among those shown in FIG. 8 andFIG. 9, and the step of comparing one by one the generated comparisonvalues with the prediction error supplied to the error-to-symbolconverter 36 or the error-to-symbol converter 38. The comparisoncontinues until one of the generated comparison values coincides withthe prediction error. When one of the generated comparison values doesnot coincide with the prediction error, a binary symbol “0” is produced.Then, a next generated comparison value and the prediction error arecompared. When the next generated comparison value does not coincidewith the prediction error, a binary symbol “0” is produced again.Thereafter, when a comparison value subsequently generated coincideswith the prediction error, a binary symbol “1” is produced, and theconversion is terminated.

An operation of achieving the correspondence between the predictionerror and binary symbol(s) by using the above-mentioned algorithm willbe described more specifically with reference to FIG. 8.

Here, it is assumed that a prediction error to be supplied to theerror-to-symbol converter 36 is “−2”.

The error-to-symbol converter 36 generates “−1” as the first comparisonvalue. Since the first comparison value and the prediction errorsupplied to the error-to-symbol converter 36 do not coincide with eachother, a binary symbol “0” is output. Then, the error-to-symbolconverter 36 generates “+1” as the second comparison value. Since theprediction error “−2” and the comparison value “+1” do not coincide witheach other, a binary symbol “0” is output again. Then, theerror-to-symbol converter 36 generates the comparison value “−2”. Sincethe prediction value and the comparison value coincide with each otherthis time, a binary symbol “1” is generated, and the conversion isterminated. Consequently, when the prediction error “−2” is supplied tothe error-to-symbol converter 36, a binary symbol sequence “001” isoutput.

Next, an encoding operation of an encoding apparatus 400 according tothe first embodiment will be described.

FIG. 10 is a flow chart showing a mode deciding operation effected bythe mode determinator 2 and a flow of an encoding operation based on thedecided mode.

Referring to FIG. 10, a mode switching operation is effected by the stepof deciding by the mode determinator 2 whether or not reference pictureelements a, b, and c for an encoding picture element which have beensupplied from the picture element memory 1 satisfy the condition “a=b=c”(“a=b=c” indicates the values of reference picture elements a, b, and care all identical) (S16), and the step of deciding whether the outputvalue of the zero determinator 4 is “0” (prediction error=0; orprediction has proved to be correct) or “1” (prediction error≈0; orprediction has proved to be incorrect) (S15). Then, the mode A or themode B is specified (at S17 and S98). If the condition “a=b=c” issatisfied (at S11 or S16), and if the output value of the zerodeterminator 4 is then determined to be “0” (at S15), encoding in themode A is determined and continues (at S18). In other words, oncereference picture elements a, b, and c adjacent to a picture element Xhave satisfied the condition “a=b=c”, the encoding in the mode Acontinues until a picture element X which does not coincide with aprediction value X occurs. If the output value of the zero determinator4 is determined to be “1” (at S15), the picture element which hasrendered the output value of the zero determinator 4 “1” is encoded inthe mode A. Then, the mode B is set, and the encoding mode is switchedinto the mode B (at S17). When the condition “a=b=c” is satisfied in themode B (at S16), the mode A is set (at S98). Then, whether the outputvalue of the zero determinator 4 is “0” (the prediction error=0; or theprediction has proved to be correct) or “1” (the prediction error≈0; orthe prediction has proved to be incorrect) is determined (at S15). Ifthe condition “a=b=c” is not satisfied in the mode B, encoding in themode B is implemented and continues (at S19).

The operations of the flow chart shown in FIG. 10 will be hereinafterdescribed again by referring to specific examples about FIG. 5 and FIG.6.

(1) Encoding in the Mode A

An encoding operation in the mode A will be described.

First, the zero determinator 4 outputs a binary symbol “0” if aprediction error obtained by subtracting the output of the predictor 3or the prediction value (for example, the value of the picture elementwhich has been output immediately before the reference picture element)from the value of an encoding picture element is zero (the predictionhas proved to be correct). On the other hand, if a prediction error isnot zero (the prediction has proved to be incorrect), the zerodeterminator 4 outputs a binary symbol “1”. The first encoder 5implements encoding, regarding the output value “0” of the zerodeterminator 4 as the MPS and the output value “1” as the LPS. Theencoding process in case that the output value of the zero determinator4 is “0” (a prediction error is zero), and in case that the output valueof the zero determinator 4 is “1” (a prediction error is not zero)proceeds as follows:

(1-1) Case that the output value of the zero determinator 4 is “0”.

The first encoder 5 has an MPS counter (not shown) inside theprobability estimator 25. The MPS counter counts the number of binarysymbols “0” indicating that a prediction error is zero, that is, thenumber of MPSs consecutively occurred. As is seen from FIG. 67, aone-bit codeword “0” is determined only when the number of MPSsconsecutively occurred which are supplied to the first encoder 5 (thecount of the MPS counter) has become equal to the code order. Thecodeword is not determined until the number of MPSs consecutivelyoccurred becomes equal to the code order.

(1-2) Case that the output value of the zero determinator 4 is “1”.

First, the first encoder 5 encodes a binary symbol “1” indicating that aprediction error is not zero, that is, an LPS together with the numberof MPSs which have occurred before the LPS and which have not beenallotted a codeword yet. As seen from FIG. 67, the codeword length isdetermined according to the number of MPSs which have occurred beforethe LPS (the count of the MPS counter). When the code order is 2^(n) acodeword whose codeword length is (n+1) bits is determined. Whenencoding by the first encoder 5 is finished, the second encoder 6converts a prediction error obtained by subtracting the prediction valueoutput of the predictor 3 from the value of an encoding picture element(−255˜−1, 1˜255, exclusive of zero, in the case of one picture elementbeing represented by eight bits) into a binary symbol sequence “0 . . .01” shown in FIG. 8 so as to implement encoding. The converted binarysymbol sequence is divided into at least one message based on the valueof the code order determined by the probability estimator 26. Then, thecodeword corresponding to the at least one message is determined.

The feature of this embodiment is that, when a prediction error isencoded by the second encoder 6, the same encoding system as that hasbeen applied to the first encoder 5 as shown in FIG. 67 is also applied.In other words, a main feature of this embodiment is that, for encodinga binary symbol sequence, the same encoding method shown in FIG. 67 isapplied to both the first encoder 5 and the second encoder 6.

(2) Encoding in the Mode B

Next, an operation of encoding in the mode B will be described.

The predictor 7 calculates a prediction value from the value of at leastone reference picture element. The calculation method may be implementedin accordance with a predetermined prediction function or by referringto the reference table. The third encoder 8 converts a prediction error(−255˜+255, inclusive of zero in the case of one picture element beingrepresented by eight bits) obtained by subtracting the calculatedprediction value from the value of an encoding picture element into abinary symbol sequence shown in FIG. 9. Then, the third encoder 8encodes the binary symbol sequence in the same manner as that with thesecond encoder 6. In other words, a codeword corresponding to the binarysymbol sequence is generated, based on the encoding method illustratedin FIG. 67. Since all of binary symbol sequences shown in FIG. 9 endwith an LPS, the third encoder 8 can determine codewords correspondingto all the binary symbol sequences illustrated in FIG. 9.

In the conversion examples shown in FIG. 8 and FIG. 9 describedhereinbefore, the values which would most likely occur as predictionerrors are successively generated and compared with a prediction errorshown in FIG. 8 or FIG. 9. When one of these values coincides with theprediction error, a binary symbol “1” is output. While on the otherhand, when one of these values does not coincide with the predictionerror, a binary symbol “0” is output. In this way, prediction errors areconverted into binary symbol(s). As described hereinbefore, theerror-to-symbol converter 36 and the error-to-symbol converter 38convert a prediction error into binary symbol(s) and supplies the binarysymbol(s) to the probability estimator 26 and the probability estimator28, respectively. The probability estimator 26 and the probabilityestimator 28 receive the binary symbol(s), change, and determine thecode order based on the received binary symbol(s) and supplies thedetermined code order to the codeword allotter 16 and the codewordallotter 18, respectively. The aforementioned two code orderdetermination methods can be applied in this case. Encoding effected bythe codeword allotter 16 and the codeword allotter 18 are the same asencoding effected by the codeword allotter 15. It means that encoding isaccomplished by using the encoding method shown in FIG. 67.

Referring again to FIG. 4, the encoding controller 11 directs thepicture element memory 1 to store the values of encoding pictureelements and output the values of the encoding picture elements and thevalue of at least one reference picture element adjacent to one of theencoding picture elements. The encoding controller operates the firstencoder 5, the second encoder 6, and the third encoder 8 appropriatelyvia the mode discrimination signal CM supplied from the modedeterminator 2. During that operation process, the first encoder 5, thesecond encoder 6, and the third encoder 8 notify the encoding controller11 of the state in which codewords are arranged to be output. Theencoding controller 11 determines among the first encoder 5, the secondencoder 6, and the third encoder 8 the encoder for outputting codewordsand uses the code switching device 9 and the code buffer 10 to supply acode composed of a sequence of codewords in the order that the codewordshave been determined. By being directly notified of required individualcodeword lengths from the first encoder 5, the second encoder 6, and thethird encoder 8, or by being indirectly notified of the requiredindividual codeword lengths via the encoding controller 11, the codebuffer 10 constitutes a code from codewords.

Next, referring to FIG. 11 and FIG. 12, the flow chart illustrated inFIG. 10 will be more specifically described.

FIG. 11 is a diagram showing encoding picture elements, the condition ofreference picture elements, the output values of the zero determinator,and prediction errors.

When picture elements X₁ through X₆ as shown in FIG. 11 have beenentered, the condition of reference picture elements adjacent to themare as described in FIG. 11. The output values of the zero determinatorindicate whether or not predictions for respective encoding pictureelements have proved to be correct. Prediction errors represent thevalues of the prediction errors when predictions have proved to beincorrect. Assuming that the picture elements X₁ through X₆ as shown inFIG. 11 are entered successively, the operations of the flow chartillustrated in FIG. 10 will be described. The results obtained from theoperations are shown in FIG. 12. For simplifying the description, it isassumed in FIG. 12 that all of the probability estimators 25, 26, and 28provided in the first encoder 5, the second encoder 6, and the thirdencoder 8, respectively had determined the code order to be four(2^(n)=4).

In the initial state when power has been supplied to the apparatus, themode A is set as the initial encoding mode for the apparatus at S11.Then, at S12, the picture element X₁ is entered. At S14, the pictureelement X₁ is determined to be encoded in the mode A, and at S15, theoutput value of the zero determinator for the picture element X₁ ischecked. As shown in FIG. 11, the output value of the zero determinatorfor the picture element X₁ is zero. Thus, the operation proceeds to S18.At S18, the picture element X₁ is encoded in the mode A by the firstencoder 5.

Next, at S12, the picture element X₂ is entered. Through S14, S15, andS18, the picture element X₂ is also encoded in the mode A.

Next, at S12, the picture element X₃ is entered. Then, at S14, thepicture element X₃ is determined to be encoded in the mode A, and theoperation proceeds to S15. At S15, since the output value of the zerodeterminator is 1, the operation proceeds to S17. At S17, the pictureelement X₃ is encoded in the mode A. Since the output value of the zerodeterminator is one, encoding in the mode A in this case is effected bythe first encoder 5 and the second encoder 6. Since an LPS has occurred,the codeword supplied from the first encoder 5 for the picture elementsX₁, and X₂ is determined. In FIG. 12, the codeword supplied from thefirst encoder 5 for the picture elements X₁, and X₂ is completed in aposition P1. As described hereinbefore, when encoding in the mode A isdetermined by the occurrence of an LPS encoding by the second encoder 6is effected for the picture element for which the output value of thezero determinator is “1”. As shown in FIG. 11, the prediction error ofthe picture element X₃ is “+1”. Accordingly, the error-to-symbolconverter 36 in the second encoder 6 outputs binary “01” symbolsaccording to the table shown in FIG. 8. The second encoder 6 encodes thebinary symbols according to the encoding method shown in FIG. 67. Allthe binary symbols shown in FIG. 8 end with an LPS. For this reason,when using the encoding method shown in FIG. 67 and when encoding ofindividual prediction errors shown in FIG. 8 is finished by the secondencoder 6, the codewords corresponding to the individual predictionerrors are always determined. As shown in FIG. 12, in the case of thepicture element X₃, the codeword supplied from the second encoder 6 forthe picture element X₃ is determined in a position P2.

Next, at S17, the mode B is set. Then, at S12, the picture element X₄ isentered. At S14, the picture element X₄ is determined to be encoded inthe mode B. Then, at S16, the state of the reference picture elementsfor the picture element X₄ is checked. As shown in FIG. 11, since thevalues of the reference picture elements for the picture element X₄ donot satisfy the condition “a=b=c”, the operation proceeds to S19. Then,at S19, the picture element X₄ is encoded in the mode B. Since theprediction error of the picture element X₄ is “+1”, binary symbols “001”are output as shown in FIG. 9. All the binary symbol sequences shown inFIG. 9 also end with an LPS. For this reason, as long as the encodingmethod shown in FIG. 67 is used, codewords supplied from the thirdencoder 8 are determined at the end of the encoding operation forindividual prediction errors. As shown in FIG. 12, the codeword for thepicture element X₄ is determined in a position P3.

After the codeword for the picture element X₄ has been determined atS19, the picture element X₅ is entered at S12. The picture element X₅ isdetermined to be encoded in the mode B at S14, and the state of thereference picture elements for the picture element X₅ is checked at S16.Since the reference picture elements a, b, and c for the picture elementX₅ satisfy the condition “a=b=c”, the mode A is set (at S98). Then, theoperation proceeds to S15. As the output value of the zero determinatorfor the picture element X₅ is zero, the operation proceeds to S18. AtS18, the picture element X₅ is encoded in the mode A. At this point, thecodeword supplied from the first encoder 5 for the picture element X₅has not been determined yet.

Next, the picture element X₆ is entered at S12. At S14, the pictureelement X₆ is determined to be encoded in the mode A. At S15, the outputvalue of the zero determinator for the picture element X₆ is determinedto be “1”. Accordingly, the picture element X₆ is encoded in the mode Aat S17. Since an LPS has occurred in the case of the picture element X₆,the codeword supplied from the first encoder 5 for the picture elementX₅ is determined in a position P4, as shown in FIG. 12. Since the firstencoder 5 determines the codeword for the picture element X₅ due to anLPS occurred, the second encoder 6 encodes the prediction error for thepicture element X₆. As shown in FIG. 11, the prediction error for thepicture element X₆ is “−2”. Accordingly, as shown in FIG. 8, the binary“001” symbols for the prediction error of “−2” are to be encoded. Sincean LPS has occurred in a position P5, the codeword supplied from thesecond encoder 6 for the picture element X₆ is determined in theposition P5.

Determined codewords shown in FIG. 12 indicate the case where theprobability estimators 25, 26, and 28 in the first encoder 5, the secondencoder 6, and the third encoder 8, respectively determine the codeorder to be four (2^(n)=4) as shown in FIG. 67. For simplifying thedescription, it is assumed herein that all the first encoder 5, thesecond encoder 6, and the third encoder 8 implement encoding with thecode order four. However, as described hereinbefore, the first encoder5, the second encoder 6, and the third encoder 8 respectively determinetheir own code orders and operates independently.

As described above, in this embodiment, a picture element is entered,and the code for the entered picture element is output. The output codeis temporarily stored in a memory (not shown) in the code buffer 10.Then, the output code is transmitted from the code buffer 10 directly orindirectly via radio or a communications line in analog or digitalformat. Alternatively, the output code is stored in a storing medium(such as a magnetic or optical recording card, a tape, a disc, a RAM, ora ROM).

In this first embodiment, when the encoding mode is switched from themode A to the mode B, an LPS is always output. That is, in this firstembodiment, when the encoding mode is switched from the mode A to themode B, a codeword is always determined by the first encoder 5 or thesecond encoder 6. When the encoding mode is switched from the mode B tothe mode A, an LPS is also always output. For this reason, in this firstembodiment, when the encoding mode is switched from the mode B to themode A, a codeword is always determined by the third encoder 8.

As described above, when MPSs consecutively occur, this encodingapparatus provides a considerably enhanced encoding efficiency. Byswitching the encoding mode into the mode B when an LPS has occurred inthe mode A, and by switching the encoding mode from the mode B to themode A when the values of reference picture elements a, b, and c havesatisfied a predetermined condition “a=b=c” in the mode B, switching ofencoding between the first encoding section and the second encodingsection is actively implemented.

In this way, switching of encoding in the first encoding section and thesecond encoding section is implemented appropriately and consistently.Thus, efficient encoding and decoding can be implemented. Switching ofencoding is effected by the encoding controller 11 which controlsrespective devices within the encoding apparatus, using the modediscrimination signal CM and the control signals C1 through C6.

FIG. 13 is a block diagram showing a configuration of a decodingapparatus 500 according to the first embodiment of the presentinvention.

First, the configured elements of the decoding apparatus 500 accordingto the first embodiment will be described.

Reference numeral 41 indicates a picture element memory for outputtingat least one stored and decoded picture element adjacent to a decodingpicture element as reference picture element before decoding thedecoding picture element. The picture element memory 41 also storesdecoded picture elements.

Reference numeral 42 indicates a mode determinator, like the modedeterminator 2 in the encoding apparatus described hereinbefore, fordetermining the decoding mode to be either the mode A or the mode B,based on the value of the at least one reference picture element. Then,the mode determinator 42 outputs the mode discrimination X signal CM.

Reference numeral 45 indicates a first decoder for decoding a codewordin the mode A into a binary symbol indicating whether or not aprediction error is zero. (When the zero determinator determines whethera prediction error is one or not one, for example, the first decoderdecodes a codeword in the mode A into a binary symbol indicating whetheror not a prediction error is one. Similarly, when the determinatordetermines whether a prediction error is −3 or not −3, the first decoderdecodes a codeword in the mode A into a binary symbol indicating whetheror not a prediction error is −3.)

Reference numeral 46 indicates a second decoder for decoding a codewordin the mode A into a prediction error when the prediction error is notzero.

Reference numeral 48 indicates a third decoder for decoding in the modeB a codeword into a prediction error between the value of a decodingpicture element and the prediction value calculated by the predictor 7for the decoding picture element.

Reference numeral 40 indicates a code buffer for dividing an input codeinto codewords and outputting the codewords.

Reference numeral 43 indicates a decoding controller for controlling thepicture element memory 41, the first decoder 45, the second decoder 46,and the third decoder 48, a picture element switching device 12 (whichwill be described hereinafter), and the code buffer 40 based on the modediscrimination signal CM and the control signals C11 through C16.

Reference numeral 12 indicates the picture element switching device forselecting an appropriate decoded picture element among decoded pictureelements output from decoding picture element calculators 32 and 33, andthe predictor 3, and outputting the value of the appropriate decodedpicture element.

Reference numerals 32 and 33 indicate the first decoding picture elementcalculator and the second decoding picture element calculator,respectively for calculating the value of a decoding picture elementfrom the prediction value for the decoding picture element and thedecoded prediction error.

The predictor 3 and the predictor 7 are the same as those in the pictureencoding apparatus described hereinbefore.

Reference numeral 201 indicates a first decoding section provided withthe first decoder 45 for decoding a codeword into a binary symbolindicating whether or not a prediction error between the value of adecoding picture element and the estimated prediction value is zero, andthe second decoder 46 for decoding a codeword into a prediction errorwhen the prediction error is not zero.

Reference numeral 202 indicates a second decoding section provided withthe third decoder 48 for decoding a codeword into a prediction errorregardless of whether the prediction error between the value of adecoding picture element and the estimated prediction value is zero ornot.

FIGS. 14, 15, and 16 are block diagrams respectively showing an internalconfiguration of the first decoder 45, the second decoder 46, and thethird decoder 48.

The first decoder 45, the second decoder 46, and the third decoder 48have a first symbol restoring device 55, a second symbol restoringdevice 56, and a third symbol restoring device 58, respectively.Furthermore, the first decoder 45, the second decoder 46, and the thirddecoder 48 have a first probability estimator 75, a second probabilityestimator 76, and a third probability estimator 78, respectively. Thesecond decoder 46 and the third decoder 48 have a first symbol-to-errorconverter 86 and a second symbol-to-error converter 88 respectively forconverting a binary symbol sequence to a prediction error.

Next, a decoding operation of the decoding apparatus according to thisembodiment will be described.

The first decoder 45, the second decoder 46, and the third decoder 48receive codewords into which the code buffer 40 has divided a code andwhich have been supplied from the code buffer 40. When the first decoder45, the second decoder 46, or the third decoder 48 implements decodingwith the code order 2^(n), the first decoder 45, the second decoder 46,or the third decoder 48 determine the codeword length based on the valueof the starting bit of a codeword in the following way:

When the value of the starting bit of a codeword is zero, the codewordlength is determined to be 1. Consequently, as seen from FIG. 67, amessage comprised solely of binary symbols “0” having the codewordlength 2^(n) is restored. When the value of the starting bit of acodeword is 1, the codeword length is determined to be (n+1) bits.Consequently, the first decoder 45, the second decoder 46, or the thirddecoder 48 regards the value of the binary symbols for the remainingn-bit codeword except the starting bit 1 of the codeword as k or thenumber of binary symbols “0” consecutively occurred. Then, a message “0. . . 01” having the codeword length of (k+1) bits is restored.

When decoding in the mode A, the first decoder 45 receives a codeword,converts the codeword into a binary symbol sequence, and outputs thebinary symbol sequence (which is equivalent to a message). Each outputof the first decoder 45 is for a picture element which is to be decodedin the mode A. When the output value of the first decoder 45 is “0”, itindicates that a prediction error for a decoding picture element iszero. On the other hand, when the output value of the first decoder 45is “1”, it indicates that a prediction error is not zero. When aprediction error is zero, the prediction value will become the value ofa decoding picture element. When a prediction error is not zero, theprediction error is subsequently decoded by the second decoder 46.

When decoding a prediction error, the second decoder 46 and the thirddecoder 48 respectively receive codewords and convert the codewords intoat least one message. Then, the second decoder 46 or the third decoder48 combine the at least one message into binary symbol sequences. Thesecond decoder 46 implements decoding in the mode A for a pictureelement for which the prediction error is not zero. The second decoder46 inversely converts a binary symbol sequence, which is as shown inFIG. 8 (which indicates the case that a prediction error of zero doesnot exist), into a prediction error and outputs the prediction error.The third decoder 48 implements decoding for a picture element which hasbeen encoded in the mode B. The third decoder 48 inversely converts abinary symbol sequence, which is as shown in FIG. 9 (which indicates thecase that a prediction error of zero exists), into a prediction errorand outputs the prediction error. The value of a decoding pictureelement which is to be decoded in the mode A is obtained by adding theoutput of the predictor 3 (the prediction value) to the output of thesecond decoder 46 (the prediction error). The value of a decodingpicture element which is to be decoded in the mode B is obtained byadding the output of the predictor 7 (the prediction value) to theoutput of the third decoder 48 (the prediction error).

Mode switching in a decoding process can be implemented by the modedeterminator 42, by using the same determination method as with the modedeterminator 2 shown in FIG. 4, based on the condition of referencepicture element(s) output from the picture element memory 41 and theoutput value of the first decoder 45.

While the decoding process is being implemented, the decoding controller43 directs the picture element memory 41 to output at least onereference picture element, and also operates the first decoder 45, thesecond decoder 46, and the third decoder 48 selectively according to themode discrimination signal CM output from the mode determinator 42.During this process, the first decoder 45, the second decoder 46, andthe third decoder 48 notify the decoding controller that a codeword hasbeen input. By being directly notified of the individual codewordlengths or by being indirectly notified of the individual codewordlengths via the decoding controller 43, the code buffer 40 divides acode into codewords. The decoding controller 43 determines theappropriate decoder for implementing decoding among the first decoder45, the second decoder 46, and the third decoder 48 and directs thepicture element switching device 12 to supply decoded picture elementsto the picture element memory 41 for storing them.

Embodiment 2

FIG. 17 is a block diagram showing a configuration of an encodingapparatus 400 according to the second embodiment of the presentinvention. FIG. 17 is different from FIG. 4 described in the firstembodiment, in that the output of the zero determinator 4 is notsupplied to the mode determinator 2.

An operation of the encoding apparatus 400 according to this embodimentwill be described.

In this embodiment, as shown in FIG. 18, when the values of referencepicture elements a, b, and c adjacent to an picture element X satisfythe condition “a=b=c”, the picture element X is encoded in the mode A(at S4 through S6). When the values of reference picture elements a, b,and c do not satisfy the condition, the picture element X is encoded inthe mode B (at S7). The mode determinator 2 implements this modeswitching operation just by determining whether or not the values ofreference picture elements a, b, and c from the picture element memory 1satisfy the condition “a=b=c”. There is not a case that the output valueof the zero determinator 4 is referred to as in the first embodiment.Since encoding operations in the mode A and the mode B are same as thosein the first embodiment, the description about the encoding operationswill be omitted.

In the first embodiment, when the encoding mode is switched from themode A to the mode B, a codeword is always determined by the firstencoder 5. In the second embodiment, since the condition for determiningthe encoding mode is different from that in the first embodiment, acodeword is not always determined by the first encoder 5.

FIG. 19 shows an example of binary symbols into which picture elementsX₁ through X₆ are encoded according to the second embodiment of thepresent invention. The example shown in FIG. 19 shows the encoding statewhere the encoding picture elements shown in FIG. 11 are input into theencoding apparatus according to this embodiment. For simplifying thedescription, it is assumed herein that a codeword is supplied from thefirst encoder 5, the second encoder 6, and the third encoder 8 forimplementing encoding with the code order four. Referring to the exampleshown in FIG. 19, at the time of termination of the encoding for thepicture element X₂ in the mode A, binary symbols output consecutivelyhave not ended with 1. The count of the MPS counter has not reached thecode order four, either. For this reason, a codeword for the pictureelement X₂ is not determined by the first encoder 5. Thus, before thecodeword for the picture element X₂ is determined by the first encoder5, codewords for the picture elements X₃ and X₄ are determined by thethird encoder 8. In this case, the decoding apparatus 500 cannotimplement accurate decoding unless a codeword generated by the firstencoder 5 is input into the decoding apparatus before a codewordgenerated by the third encoder 8 is input into the decoding apparatus.For this reason, an operation for changing the transmission order ofcodewords which will be described hereinafter, that is, control over thetransmission order of codewords is required in the encoding apparatus400. Alternatively, a picture-element preread operation in the mode A,which will be described hereinafter, is required in the encodingapparatus 400.

First, an operation for controlling the transmission order of codewordsaccording to the second embodiment of the present invention will bedescribed with reference to FIG. 20 and FIG. 21.

FIG. 20 is a flow chart showing a flow of the control processimplemented by the encoding controller 11 after a codeword has beendetermined by the third encoder 8 (at S20).

FIG. 21 is a flow chart showing a flow of the control processimplemented by the encoding controller 11 after a codeword has beendetermined by the first encoder 5 (at S30).

In this embodiment, control over the transmission order of codewords isrequired when a codeword has been generated by the third encoder 8before a codeword is determined by the first encoder 5, as shown in FIG.19 (in other words, when the count of the MPS counter inside the firstencoder 5 is equal to or greater than one at S22 in FIG. 20), a codewordis determined by the third encoder 8. In this case, the codewordgenerated by the third encoder 8 is temporarily stored in the codebuffer 10 (at S24 in FIG. 20). In the following two cases, a codeword isdetermined by the first encoder 5:

(1) When the number of MPSs consecutively occurred has become equal tothe code order.

(2) When an LPS has occurred.

As shown in FIG. 21, both in the cases (1) and (2), transmission of acodeword determined by the first encoder 5 and transmission of acodeword determined by the third encoder 8 and temporarily stored in thecode buffer 10 are implemented in the inverse order. Thus, after thecodeword determined by the first encoder 5 has been transmitted, thecodeword temporarily stored in the code buffer 10 is transmitted by adirection of the encoding controller 11 (at S34). As shown at S35 andS36 in FIG. 21, in the case (2), after a codeword determined by thefirst encoder 5 and a codeword temporarily stored in the code buffer 10have been transmitted (at S34), a codeword determined by the secondencoder 6 is further transmitted (at S36). Referring to the exampleshown in FIG. 19, codewords are determined by the third encoder 8 inpositions P1 and P2. While on the other hand, a codeword which is to beoutput from the first encoder 5 is determined in a position P3.Consequently, the codewords determined by the third encoder 8 in thepositions P1 and P2 are temporarily stored in the code buffer 10. When acodeword to be output from the first encoder 5 has been determined inthe position P3, the codeword determined in the position P3 is outputfirst. Then, the codewords temporarily stored in the code buffer 10 anddetermined in the positions P1 and P2 are output subsequently. Finally,a codeword determined by the second encoder 6 in a position P4 isoutput.

In the case (2), as is shown at S44 in FIG. 22, a codeword determined bythe first encoder 5, a codeword determined by the second encoder 6, anda codeword determined by the third encoder 8 and temporarily stored inthe code buffer 10 can be transmitted in stated order. According to aflow chart illustrated in FIG. 22, the output order of codewords shownin FIG. 19 is such that a codeword determined by the first encoder 5 inthe position P3 is output first. Then, a codeword determined by thesecond encoder 6 in the position P4 is output. Then, a codeworddetermined by the third encoder 8 in the position P1 is output. Finally,a codeword determined by the third encoder 8 in the position P2 isoutput.

When controlling the transmission order of codewords, a maximum capacityMAX of the code buffer 10 needs to be determined both by thetransmitting side and the receiving side.

FIG. 23 shows an operation for defining the maximum capacity MAX of thecode buffer 10.

When the picture elements X₀ through X₂ have been encoded in the mode A,codewords corresponding to the picture elements X₁ through X₂ have notbeen determined, and the encoding mode has been switched into the modeB, and when codewords have been determined in the mode B and in theposition P1, the position P2, and the position P3, etc. one afteranother and have been temporarily stored in the code buffer 10, the codebuffer 10 sequentially stores the temporarily stored codewordsdetermined by the third encoder 8. In this situation, the maximumcapacity MAX of the code buffer 10 occupied by the temporarily storedcodewords should be defined. When the number of temporarily storedcodewords has reached the maximum capacity MAX of the code buffer 10,the temporarily stored codewords should be output so as to increase thevacant area of the code buffer 10. As shown in FIG. 23, when the numberof temporarily stored codewords has reached the maximum capacity MAX inthe position P4 of the code buffer 10, dummy binary symbols “0” whosenumber is equal to the number required for determining a codeword in themode A should be added to binary symbols for which a codeword has notbeen determined. Since FIG. 23 shows a case where the code order isfour, two dummy binary symbols “0” are added. Then, the codeword to beoutput from the first encoder 5 is determined. Dummy binary symbols “0”are added to binary symbols for which a codeword has not been determinedby the required number until the codeword is determined by the firstencoder 5.

By determining a codeword to be output from the first encoder 5 by forcein this way, codewords determined by the third encoder 8 and temporarilystored in the code buffer 10 are output. Consequently, a vacant area forthe code buffer 10 can be regained. By implementing the processdescribed above, an overflow of the code buffer 10 by the temporarilystored codewords determined by the third encoder 8 can be prevented.

Even if dummy binary symbols “0” are added to binary symbols for which acodeword has not been determined in the above-mentioned way, an accuratedecoding operation can be effected by setting the maximum capacity MAXof the code buffer in the decoding apparatus 500 to be identical to thatin the encoding apparatus 400 and by implementing a process of addingdummy binary symbols “0”.

FIG. 23 shows a case where dummy binary symbols “0” are added to binarysymbols for which a codeword has not been determined so as to determinea codeword to be output from the first encoder 5. Alternatively, acodeword to be output from the first encoder 5 may be determined byadding only a dummy binary symbol “1” to the binary symbols. In thiscase, however, a codeword for a prediction error should not be generatedfrom the second encoder 6 when a dummy binary symbol “1” has been added.

Next, a picture element preread operation in the encoding mode A will bedescribed with reference to FIG. 24.

The term “picture element preread operation in the encoding mode A” usedherein is employed to mean an operation for reading the values ofpicture elements to be encoded subsequently one by one beforehand untila codeword to be output from the first encoder 5 is determined.

FIG. 24 is a flow chart showing a flow of the control process initiatedby the encoding controller 11 after the mode B has been set (at S50).

According to the picture element preread operation in the encoding modeA, after the mode B has been set at S50 as shown in FIG. 24, whether ornot the count of the MPS counter inside the first encoder 5 is zero ischecked at S52. When the count of the MPS counter is zero, it means thata codeword to be output from the first encoder 5 has already beendetermined. Thus, the picture element preread operation is not required.When the count of the MPS counter inside the first encoder 5 is notzero, it means that a codeword to be output from the first encoder 5 hasnot been determined. For this reason, the picture element prereadoperation shown at S53 through S56 will be implemented. That is, until acodeword to be output from the first encoder 5 is determined (at S55),the values of picture elements to be encoded subsequently are preread(at S53) one by one and the picture element preread operation (at S53through S56) is repeated over and over again. Then, after a codeword forthe picture element to be output from the first encoder 5 has beendetermined, encoding in the mode B is implemented (at S57) for thepicture elements which have not been encoded due to the picture elementpreread operation. Referring again to FIG. 19, in order to implement thepicture element preread operation, the encoding mode for the pictureelements following the picture element X₂ should not be switched fromthe mode A to the mode B. Instead of doing this, the values of thepicture elements X₅ and X₆ are preread so as to determine codewords tobe output from the fist encoder 5 (at 555). Thereafter, the pictureelements X₃ and X₄ which have not been encoded yet are encoded in themode B (at S57). When implement the picture element preread operation,the values of the picture elements to be encoded subsequently are to bepreread. Thereafter, encoding should be implemented for the pictureelements which have not been encoded yet due to the picture elementpreread operation. For this reason, a line memory for storing pictureelements is needed, and both the transmitting side and the receivingside need to predefine the maximum capacity of the line memory. Thereason for predefining the maximum capacity of the line memory is thesame as that given from FIG. 23. That is, because, even if pictureelements to be encoded subsequently are preread for a codewordundetermined by the first encoder 5, it occurs that a codeword may stillbe undetermined by the first encoder 5. Thus, the maximum capacity ofthe line memory for storing picture elements should be predefined. Ifthe number of picture elements is to exceed the maximum capacity of theline memory, dummy binary symbols “0” are added to binary symbols forwhich a codeword has not been determined yet so as to determine thecodeword to be output from the first encoder 5. As describedhereinbefore, a dummy binary symbol “1” may be added to determine thecodeword to be output from the first encoder 5.

Next, a configuration of a decoding apparatus 500 according to the thisembodiment will be described with reference to FIG. 25. FIG. 25 isdifferent from FIG. 13 used in the first embodiment in that the outputof the first decoder 45 is not supplied to the mode determinator 42. Thefirst decoder 45 shown in FIG. 25 implements the same decoding operationas that of the first decoder 45 shown in FIG. 13 according to the firstembodiment. That is, the first decoder 45 decodes a codeword in the modeA into a binary symbol indicating whether or not a prediction error iszero. Then, the result is transmitted to the decoding controller 43through the control signal C13. The decoding controller 43 operates thesecond decoder 46 based on the information from the first decoder 45 asto whether or not the prediction error is zero. Hereinafter, adescription will be especially directed to an operation different fromthat according to the first embodiment of the present invention.

The decoding apparatus 500 according to this embodiment converts aninput codeword into a binary symbol sequence (or a message). Using suchmessages, the values of picture elements are reproduced. In this secondembodiment, as different from the first embodiment, there is a case thatthe decoding mode is switched from the mode A into the mode B before allof the binary symbols into which the first decoder 45 decodes onecodeword in the mode A are used up. Referring again to FIG. 19, whendecoding X₁ binary symbols 0001 associated with decoding of X₂, X₅, andX₆ can be obtained. However, after X₂ is decoded, the decoding mode isswitched into the mode B. Thus, binary symbols “01” remain unused. Theunused binary symbols “01” will be used after decoding in the mode B hasbeen finished. Thus, when unused binary symbols to be decoded in themode A remain in the first decoder 45, the decoding controller 43directs the first decoder 45 to output the unused binary symbols. Whenno unused binary symbol is not present in the first decoder 45, thedecoding controller 43 directs the first decoder 45 to receive acodeword, converts it into a sequence of binary symbols, and decodes thebinary symbols.

In the decoding apparatus 500, as described above, except that anoperation for controlling the order in which decoded binary symbols areto be used is needed, other operations are the same as those in thefirst embodiment. Thus, the description about them will be omitted.

As described above, according to this embodiment, the encoding mode fora picture element can be determined solely by the state to whichreference picture elements belong. Consequently, a codeword may not bedetermined when the encoder is switched from the first encoder 5 to thethird encoder 8. However, by exercising the above-mentioned control, thedecoding apparatus 500 can decode codewords into picture elementsconsistently. When the decoder is switched from the third decoder 48 tothe first decoder 45, as described in the first embodiment, a codewordis always determined as long as binary symbols shown in FIG. 9 areencoded according to the encoding method shown in FIG. 67. Thus, controlover the transmission order of codewords and control over the pictureelement preread operation are not needed.

Embodiment 3

FIG. 26 shows a configuration of an encoding apparatus 400 according tothe third embodiment of the present invention. FIG. 26 is different fromFIG. 17 described in the second embodiment in that the encoders areconfigured in a different way.

FIGS. 27, 28, and 29 are block diagrams showing a configuration of thefirst encoder 5 a, the second encoder 6 a, and the third encoder 8 arespectively according to this embodiment.

The first encoder 5 a, the second encoder 6 a, and the third encoder 8 ahave exclusive OR circuits 95, 96, and 98 respectively. Each of theexclusive OR circuits 95, 96, and 98 receives a binary symbol X and anMPS (Y) supplied from probability estimators 25 a, 26 a, and 28 arespectively, performs an operation as shown in a truth table in FIG.30, and outputs an exclusive OR signal Z to the probability estimator.The MPS (Y) used herein is defined as the value of a binary symbol whichthe probability estimators interpret as the MPS at the time of anencoding operation, that is, “0” or “1”.

An operation of the encoding apparatus 400 according to this embodimentwill be described.

In this embodiment, the encoding mode is determined according to thesame method as that described in the second embodiment. That is, asshown in FIG. 18, when reference picture elements a, b, and c adjacentto a picture element X satisfy the condition “a=b=c”, the pictureelement X is encoded in the mode A. When the reference picture elementsdo not satisfy the condition, the picture element X is encoded in themode B.

The third embodiment is different from the second embodiment in that,when encoding is implemented according to the encoding method shown inFIG. 67, interpretation of the MPS and the LPS is changed duringtransition of states. In the first and second embodiments, the firstencoder 5 interprets the MPS as “0” (a binary symbol indicating that theprediction has proved to be correct). The second encoder 6 and the thirdencoder 8 interpret the MPS as “0” defined in FIG. 8 and FIG. 9.However, in the third embodiment, as shown in a flow chart illustratedin FIG. 30, during transition of states, when an LPS has occurred (orthe prediction has proved to be incorrect) in a state S₀ (at S72),interpretation of the MPS and the LPS is changed (at S73) and thechanged interpretation will be used thereafter. For example, let usassume that while encoding is being implemented by the first encoder 5and when the MPS is interpreted as “0”, a binary symbol “1” has occurred(or the prediction has proved to be incorrect) in the state S₀. In thiscase, a corresponding codeword is output. Then, the interpretation ofthe MPS and the LPS is changed. That is, the MPS will be interpreted as“1”, and the LPS will be interpreted as “0”. Then, codewords aregenerated on that condition. On the other hand, let us assume converselythat, while encoding is being implemented by the first encoder 5 andwhen the MPS is interpreted as “1”, a binary symbol “0” has occurred inthe state S₀. In this case, a corresponding codeword is output. Then,the MPS will be interpreted as “0” and the LPS will be interpreted as“1” thereafter.

In this way, when the prediction has proved to be incorrect in the stateS₀, the interpretation of the MPS and the LPS will be changed. This isimplemented because a proposition that the occurrence probability of theMPS should be inherently higher than that of the LPS has proved to befalse, and it can be seen that a situation in which the occurrenceprobability of the LPS is higher than that of the MPS has occurred. Oncethe interpretation of the MPS and the LPS has been changed, encoding onthat condition will continue until an LPS occurs again in the state S₀.The exclusive OR circuits 95, 96, and 98 receive the binary symbol X andthe MPS (Y) from the probability estimators 25 a, 26 a, and 28 a,respectively and outputs the exclusive OR signal Z. That is, when thebinary symbol X coincides with the MPS, the exclusive OR signalindicating a binary symbol “0” is output. When the binary symbol X doesnot coincide with the MPS, the exclusive OR signal indicating a binary“1” is output. Regardless of whether the MPS is interpreted as “0” or“1”, the same rule as described hereinbefore for the transition ofstates is applied. In other words, the exclusive OR signal Z, which isthe output of the exclusive OR circuit is regarded to represent a binarysymbol for determining the transition of states described in the firstand second embodiments. Thus, the transition of states can beimplemented based on the exclusive OR signal Z.

Described above is the case where the interpretation of the MPS and theLPS is changed by using the state transition method which has beendescribed as the first example of the methods of determining the codeorder. The change in the interpretation of the MPS and the LPS can alsobe implemented easily by comparing N(0) and N(1) in the 0/1 countingmethod which has been described hereinbefore as the second example ofthe methods of determining the code order. That is, if N(0)>N(1), theMPS may be interpreted as “0”, and the LPS may be interpreted as “1”. Onthe other hand, if N(0)<N(1), the MPS may be interpreted as “1”, and theLPS may be interpreted as “0”.

Because of the change in the interpretation of the MPS and the LPS, themethod of controlling the transmission order of codewords will bedifferent from that described in the second embodiment. In the secondembodiment, when encoding is implemented by the third encoder 8 whichhas been switched from the first encoder 5, control over thetransmission order of codewords becomes possible only if it is foundwhether or not a codeword has been determined. In the third embodiment,a codeword is not always completed in the codeword completion positionshown in FIG. 19.

FIG. 31 shows how encoding is implemented when the interpretation of theMPS and the LPS has been changed.

It is assumed in FIG. 31 that in the encoders 5 a and 6 a, the MPS isinterpreted as “0” and the LPS is interpreted as “1”. It is also assumedthat in the encoder 8 a, the MPS is interpreted as “1” and the LPS isinterpreted as “0”.

The binary symbols X is converted to the exclusive OR signal Z by theexclusive OR circuit. For this reason, the encoders 5 a, 6 a, and 8 ashould receive a plurality of exclusive OR signals Z as a sequence ofbinary symbols and encode them. As shown in FIGS. 8 and 9, the binarysymbols X constitute a binary symbol sequence which always ends with anLPS. On the other hand, since the exclusive OR signal Z is the inverseof the binary symbols X, the binary symbols shown in FIG. 8 and FIG. 9are to be inverted. Thus, when the encoding mode is switched, a codewordmay not always be determined by each of the encoders. For this reason,when the encoder has been switched into the other encoder, the encodingcontroller 11 needs to know whether or not a codeword has beendetermined by the encoder which has been used before switched into theother encoder.

When a codeword has been determined by the encoder 8 a in a position P1in FIG. 31, for example, the encoding controller 11 examines if thereremains the other encoder by which a codeword has not been determined(or the encoder with the count of the MPS counter therein being equal toor greater than one). If there remains no such an encoder, the encodingcontroller 11 directs the code buffer 10 to output the determinedcodeword. If there remains the encoder by which a codeword has not beendetermined, the codeword determined by the encoder 8 a is temporarilystored in the code buffer 10. Then, the codeword determined by theencoder 8 a is output after another codeword has been determined by theother encoder. As shown in FIG. 31, a codeword to be output from theencoder 5 a has not been determined yet in the position P1. Thus, thecodeword determined in the position P1 is not output until the codewordto be output from the encoder 5 a has been determined in a position P2.Referring to FIG. 31, when the encoder is switched from the encoder 8 ato the encoder 5 a, a codeword to be output from the encoder 8 a cannotbe determined. The codeword to be output from the encoder 5 a isdetermined in the position P2, and output as described hereinbefore,before the codeword determined in the position P1 is output. Then, acodeword determined by the encoder 6 a in a position P3 is temporarilystored in the code buffer 10. Thereafter, a codeword to be output fromthe encoder 8 a is determined in the position P4. Consequently, thecodeword determined in the position P3 is output after the codeworddetermined in a position P4 is output. By implementing theabove-mentioned process, the codewords for individual messages aretransmitted in the occurrence order of the beginning symbol of theindividual messages (the order of the binary symbol which the MPScounter started to count).

Next, a configuration of a decoding apparatus 500 according to thisembodiment will be described with reference to FIG. 32.

FIGS. 33, 34, and 35 are block diagrams showing an inside configurationof decoders 45 a, 46 a, and 48 a respectively.

The decoding apparatus 500 converts an input codeword into a sequence ofbinary symbols (message), and by using the binary symbols, the value ofthe corresponding picture element is reproduced. In this thirdembodiment, before binary symbols decoded from a codeword by a decoderare used up, there is a case that binary symbols which have been decodedby the other decoder is used. When unused binary symbols have remainedin a decoder switched from the other decoder, the decoding controller 43directs the decoder to output the unused binary symbols. When unusedbinary symbols are not present in the decoder, the decoding controller43 directs the decoder to receive another codeword and decode it intobinary symbols.

In the decoding apparatus 500 according to this embodiment, control overthe order in which decoded binary symbols are to be used is exerciseddifferently from that in the second embodiment. Since other operationsare performed in the same way as in the second embodiment, thedescription about the operations will be omitted.

Embodiment 4

FIG. 36 is a block diagram showing a configuration of an encodingapparatus 400 according to the fourth embodiment of the presentinvention.

In FIG. 36, encoders 5 a, 6 a, and 8 a are encoders having the sameconfiguration as that shown in FIGS. 27, 28, and 29, respectively.

An operation of the encoding apparatus 400 according to this embodimentwill be described.

It is assumed herein that the encoding mode determination according tothis embodiment is performed in the same way as that in the firstembodiment. That is, as shown in FIG. 10, once reference pictureelements a, b, and c adjacent to a picture element X satisfy thecondition “a=b=c”, encoding is continuously implemented in the mode Auntil a picture element X becomes “X≈ a prediction value”.

The fourth embodiment is different from the first embodiment in thatwhen encoding is implemented according to the encoding method shown inFIG. 67, interpretation of the MPS and the LPS is changed duringtransition of states. According to the first and second embodiments, inthe first encoder 5, the MPS is interpreted as a binary symbol “0”(which indicates that the prediction has proved to be correct). In thesecond encoder 6 and the third encoder 8, the MPS is interpreted as “0”defined in FIG. 8 and FIG. 9. However, in the fourth embodiment,interpretation of the MPS and the LPS is changed when an LPS hasoccurred in the state S₀ at the time of the transition of states. Therule for the transition of states is applied in the same way as in thefirst, second, and third embodiments. As described hereinbefore, whenimplementing transition of states by the 0/1 counting method, the changein the interpretation of the MPS and the LPS can be implemented easilyby comparing N(0) with N(1).

Thus, the method of controlling the transmission order of codewords willbe the same as that in the third embodiment. In the second embodiment,control over the transmission order of codewords becomes possible whenit is found whether or not a codeword has been determined only when theencoder is switched from the first encoder 5 to the third encoder 8. Inthe fourth embodiment, codewords are not always completed in thecodeword completion positions P1 through P4 shown in FIG. 19. For thisreason, whenever one encoder has been switched into the other encoder,the encoding controller should know whether or not a codeword has beendetermined by the encoder which has been used before switched into theother encoder.

Next, a configuration of a decoding apparatus 500 according to thisembodiment will be described with reference to FIG. 37.

In FIG. 37, decoders 45 a, 46 a, and 48 a have the same configuration asthat of the decoders shown in FIGS. 33, 34, and 35 respectively.

The decoding apparatus 500 converts an input codeword into a sequence ofbinary symbols (message), and by using the binary symbols, the value ofa picture element is reproduced. In the fourth embodiment, before binarysymbols decoded by a decoder from a codeword are used up, there is acase that binary symbols which have been decoded by the other decoder isused. When unused binary symbols have remained in a decoder switchedfrom the other decoder, the decoding controller directs the decoder tooutput the unused binary symbols. When unused binary symbols are notpresent in the decoder, the decoding controller directs the decoder toreceive another codeword and decode it into binary symbols.

In the decoding apparatus 500 according to this embodiment, control overthe order in which decoded binary symbols are to be used is implementedin a different manner from that in the third embodiment. Since otheroperations are performed in the same way as in the third embodiment, thedescription about the operations will be omitted.

Embodiment 5

In the above-mentioned embodiments, a description has been made, basedon the assumption that each encoder has an MPS counter, a state-numbermemory for storing a state number, and an MPS memory for storing thevalue of MPSs inside. However, as shown in FIG. 38, there may be aplurality of MPS counters, state-number memories, and MPS memoriesinside the encoder. Referring to FIG. 38, a plurality of MPS countersC1, C2, C3 . . . , state-number memories R1, R2, R3 . . . , MPS memoriesQ1, Q2, Q3 . . . are present inside the encoder. MPS counters C1, C2, C3. . . , state-number memories R1, R2, R3 . . . , and MPS memories Q1,Q2, Q3 . . . are provided corresponding to the states to which referencepicture elements belong.

Even if a decoder has a plurality of MPS counters, state-numbermemories, and MPS memories corresponding to the states of referencepicture elements as described above, the decoder can be used in theaforementioned embodiments.

FIG. 39 is a block diagram showing another configuration of an encodingapparatus 400 according to the this embodiment.

When the predictor 3 and the predictor 7 described hereinbeforecalculates the prediction value of an encoding picture element by usingthe same prediction method, the predictor 3 and the predictor 7, thefirst prediction error calculator 30 and the second prediction errorcalculator 31 need not be provided separately. Alternatively, as shownin FIG. 39, the output of the prediction error calculator 30 includingthe output of the predictor 3 may be supplied to the third encoder 8.

FIG. 40 is a block diagram showing a configuration of a decodingapparatus 500 for the encoding apparatus 400 shown in FIG. 39.

Referring to FIG. 40, as in FIG. 39, only one predictor and one decodingpicture element calculator are provided in the decoding apparatus 500.

FIG. 41 is a block diagram showing another configuration of the encodingapparatus 400 according to this embodiment.

FIG. 42 is a block diagram showing an internal configuration of anencoder 5 b shown in FIG. 41.

The feature of the encoding apparatus 400 shown in FIG. 41 is that theaforementioned first encoder 5 and the second encoder 6 are combinedinto the encoder 5 b. The configuration of the encoder 5 b is as shownin FIG. 42. The encoder 5 b has a switch 85 which connects the zerodeterminator 4 to the probability estimator 25 based on the controlsignal C2. The switch 85 also connects the error-to-symbol converter 36and the probability estimator 25 based on the control signal C3. Asdescribed in the aforementioned embodiments, the first encoder 5 and thesecond encoder 6 receive different inputs, but use the same encodingmethod for encoding binary symbols. For this reason, by using theencoder 5 b as shown in FIG. 42, the configuration of an encodingapparatus can be simplified.

FIG. 43 is a block diagram showing a decoding apparatus 500 for theencoding apparatus 400 shown in FIG. 41.

FIG. 44 is a block diagram showing an internal configuration of adecoder 45 b used in the decoding apparatus 500 shown in FIG. 43.

The first decoder 45 and the second decoder 46 described in theaforementioned embodiments are combined into the decoder 45 b shown inFIG. 44.

FIG. 45 is a block diagram showing another configuration of an encodingapparatus 400 according to this embodiment.

FIG. 46 is a block diagram showing a configuration of an encoder 6 b inthe encoding apparatus 400 shown in FIG. 45.

FIG. 47 is a block diagram showing a decoding apparatus 500 for theencoding apparatus 400 shown in FIG. 45.

FIG. 48 is a block diagram showing a configuration of a decoder 46 b inthe decoding apparatus 500 shown in FIG. 47.

The feature of the encoding apparatus 400 shown in FIG. 45 is that thesecond encoder 6 and the third encoder 8 are combined into the encoder 6b. The only difference between the second encoder 6 and the thirdencoder 8 described in the aforementioned embodiments is that thecorrespondence between the prediction errors and the binary symbolsshown in FIGS. 8 and 9 becomes different. Except for this, the encoder 6b implements the same operations. Thus, as shown in FIG. 46, byswitching between the error-to-symbol converter 36 and theerror-to-symbol converter 38 by using the switch 85 in the encoder 6 b,the second encoder 6 and the third encoder 8 can be combined into theencoder 6 b. In the case of the decoder 46 b shown in FIG. 48, byswitching between the symbol-to-error converter 86 and thesymbol-to-error converter 88 by using the switch 85, the second decoder46 and the third decoder 48 shown in FIG. 13 or FIG. 25 can be combinedinto the decoder 46 b.

FIG. 49 is a block diagram showing another configuration of the encodingapparatus 400 according to this embodiment.

FIG. 50 is a block diagram showing a encoder 5 c into which the firstencoder 5, the second encoder 6, and the third encoder 8 described inthe aforementioned embodiments are combined.

The switch 85 switches between the output of the zero determinator, theoutput of the error-to-symbol converter 36, and the output of theerror-to-symbol converter 38. Thus, the encoder 5 c can have thefunctions of the first encoder 5, the second encoder 6, and the thirdencoder 8 described hereinbefore.

Though not shown in the figure in this application, the first decoder45, the second decoder 46, and the third decoder 48 can be combined intoone decoder in the same way as with the encoder 5 c.

Sixth Embodiment

FIG. 51 is a block diagram showing another configuration of an encodingapparatus 400 according to this embodiment.

The encoding apparatus 400 shown in FIG. 51 does not have the modedeterminator 2 and the second encoding section 102 provided in theencoding apparatus 400 illustrated in FIG. 4. Referring to FIG. 51, theresult of a determination which is supplied from the zero determinator 4to the mode determinator 2 is supplied to the encoding controller 11.Based on the result of the determination, the encoding controller 11uses the control signals C2 and C3 to operate the first encoder 5 andthe second encoder 6. In addition, the encoding controller 11 uses thecontrol signal C5 to operate the code switching device 9 to select anappropriate codeword from the codewords supplied from the first encoder5 and the second encoder 6 and supplies the appropriate codeword.

FIG. 52 is a block diagram showing another configuration of a decodingapparatus 500 according to this embodiment.

The decoding apparatus 500 illustrated in FIG. 52 does not have the modedeterminator 42 and the second decoding section 202 provided in thedecoding apparatus 500 illustrated in FIG. 13. A codeword is decodedinto a binary symbol representing a result of determination whichindicates whether or not a prediction error is zero by the first decoder45, and the result of the determination is supplied to the decodingcontroller 43. Based on the result of the determination received, thedecoding controller 43 uses the control signal C12 to control thepicture element switching device 12.

The feature of the encoding apparatus 400 illustrated in FIG. 51 is thatan encoding picture element is encoded based on the result of adetermination as to whether the prediction for the encoding pictureelement has been correct or incorrect. The feature of the decodingapparatus 500 illustrated in FIG. 52 is that a codeword is decoded intoa decoding picture element corresponding thereto based on the result ofa determination as to whether the prediction for the value of thedecoding picture element has been correct or incorrect. By making adetermination as to whether a prediction for an encoding or decodingpicture element has been correct or incorrect and implementing encodingor decoding of each message composed of at least one binary symbolrepresenting the result of the determination in this way, in the casehaving a high percentage of correct prediction, more efficient encodingor decoding can be implemented than in the case where a prediction erroris always encoded or a decoded.

In the above-mentioned embodiments, the predictor 3 and the predictor 7calculates a prediction value of an encoding picture element from thevalue(s) of reference picture element(s). If necessary, a predictionvalue may also be calculated based on the mode discrimination signal CM,which can be supplied to the predictor 3 and the predictor 7 from themode determinator, and the value(s) of reference picture element(s).

Although reference picture elements are assumed to be three pictureelements a, b, and c in the above-mentioned embodiments, no less thanone picture element may constitute reference picture element.

In the above-mentioned embodiments, the mode A is assumed to be selectedwhen reference picture elements a, b, and c satisfy the condition“a=b=c”. This condition may be changed according to a change in thenumber of reference picture elements. For example, when picture elementsa, b, c, and d satisfy the condition “a=b=d”, the mode A may beselected.

Although a description has not been made specifically about usingcomputer hardware or software in the above-mentioned embodiments, all ora part of the functions of the aforementioned configured elements may beimplemented by computer hardware. Alternatively, the functions of theconfigured elements may be implemented by software, or by firmware.Alternatively, by the combination of the computer hardware and software,the functions of the configured elements may be implemented.Alternatively, all or a part of the functions of the configured elementsmay be stored and implemented in a semiconductor chip.

In the above-mentioned embodiments, a description has been directed tothe case where all of the first, second, and third encoders and thefirst, second, and third decoders use the encoding method shown in FIG.67. However, when implementing encoding and decoding, the encoders andthe decoders may not use the encoding method shown in FIG. 67.

In the above-mentioned embodiments, a description has been directed tothe case where picture information is encoded or decoded. However, whenencoding or decoding audio information, optical information, or otherinformation, such encoding or decoding can be implemented in accordancewith the aforementioned embodiments. Especially when input informationtends to take a specific value, efficient encoding can be implemented.For example, when audio information or optical information contains dataextracted from the similar background to that for a picture signal, orwhen audio information or optical information contains data extractedfrom a predetermined background, the audio information or the opticalinformation can be regarded as the picture information described herein.Thus, efficient encoding can be implemented.

Embodiment 7

FIG. 53 shows a picture processing apparatus (a digital camera) as anembodiment of the picture processing apparatus according to the presentinvention. The figure shows an example of a configuration of a digitalcamera 600, which writes a static picture on a memory card.

In FIG. 53, a picture pick-up device 325 picks up a picture composed ofa plurality of picture elements, a charge coupled device (CCD) 311 isused for a sensor which converts an optical picture into an electricsignal, and the optical picture is formed on the CCD 311 through a lens312. A diaphragm 313 regulates incident dose, a shutter 314 adjusts anexposure time of the CCD 311, and an AD (Analog to Digital) converter315 converts an output of the CCD 311 into a digital signal. A framememory 316, being a semiconductor memory, temporarily stores one frameof digital signals converted from the CCD 311. A write signal processingcircuit 317 selects at least two adjacent lines of data from the outputsignals of the CCD 311 stored in the frame memory 316. The write signalprocessing circuit 317 generates a luminance signal Y, color-differencesignals U and V by an operation of signals of each picture elements andoutputs them. A picture compression circuit 318 encodes and compressesthe data of the luminance signal Y, the color-difference signals U, andV generated by the write signal processing circuit 317. A memory card319 is configured by a semiconductor memory and stores the picture. Apicture expansion circuit 320 expands the encoded picture data read fromthe memory card 319. A read signal processing circuit (or displaycircuit) 321 displays the extended luminance signal Y, and the extendedcolor-difference signals U, V on a monitor 324. A system controller 322controls an operation of the CCD 311. A trigger switch 323 startspicking up a picture.

FIG. 54 shows a sequence of writing procedure of a static picture by thedigital camera 600 shown in FIG. 53.

At time T0, the trigger switch 323 is turned ON and a static picturewriting sequence is started as will be described hereinafter. During aperiod from time T0 to time T1, dark charge accumulated in the CCD 311is removed. Next, a photometric operation is performed by a photometricelement (not shown) to set an appropriate exposure time and anappropriate exposure diaphragm. During a period from time T2 to time T3,the shutter 314 is opened and an exposure operation is performed to theCCD 311. At time T3, the shutter 314 is closed and charge of theexposure signal is read from the CCD 311. The signal read from the CCD311 is converted by the AD converter 315 into digital signal. One frameof the digital signals is temporarily stored in the frame memory 316. Attime T4, the reading operation of the exposure signal is finished.During a period from time T4 to time T5, the signal temporarily storedin the frame memory 316 is read. The luminance signal Y and thecolor-difference signals U, V are obtained from the operation of aplurality of adjacent picture elements of the CCD 311 by the writesignal processing circuit 317. The data of the luminance signal Y andthe color-difference signals U, V are encoded, compressed and stored inthe memory card 319.

FIG. 55 shows a configuration of the picture compression circuit 318.

Three encoding apparatuses 400 are provided to the picture compressioncircuit 318. The encoding apparatuses described in the above firstthrough sixth embodiments may be used for the encoding apparatuses 400.For example, the encoding apparatus 400 shown in FIG. 4 can be applied.The encoding apparatuses 400 input the luminance signal Y and thecolor-difference signals U, V in parallel from the write signalprocessing circuit 317. Each encoding apparatus implements encoding byusing the aforementioned encoding method. The encoded result is outputto the memory card 319 and stored there. As shown in FIG. 55, theluminance signal Y is one frame of luminance signals Y, having Y1, Y2, .. . , Yn. The encoding apparatus 400 inputs one frame of the luminancesignals Y and encode Y1, Y2, . . . , Yn. The color-difference signals Uand V are encoded by each encoding apparatus as well.

FIG. 56 shows a configuration of the picture expansion circuit 320.

Three decoding apparatuses 500 are provided to the picture expansioncircuit 320. The decoding apparatuses described in the above firstthrough sixth embodiments may be used for the decoding apparatuses 500.For example, the decoding apparatus 500 shown in FIG. 13 can be applied.The picture expansion circuit 320 inputs the luminance signal Y and thecolor-difference signals U, V in parallel from the memory card 319. Theluminance signal Y and the color-difference signals U, V are decoded byeach decoding apparatus 500, respectively, and output to the read signalprocessing circuit 321.

FIG. 57 shows another example of the picture compression circuit 318.

In FIG. 57, one encoding apparatus 400 is provided to the picturecompression circuit 318. The encoding apparatus 400 inputs the luminancesignal Y and the color-difference signals U, V serially frame by framefrom the write signal processing circuit 317. That is, one frame of theluminance signals Y, having Y1, Y2, . . . , Yn is input, and one frameof the color-difference signals U, having U1, U2, . . . , Un is input,and then, one frame of the difference signals V, having V1, V2, . . . ,Vn, is input. In case of FIG. 57, one encoding apparatus 400 sufficesfor the above operation, consequently, a configuration of the picturecompression circuit 318 is simplified.

FIG. 58 shows another configuration of the picture expansion circuit320.

One decoding apparatus is provided to the picture expansion circuit 320.The picture expansion circuit 320 receives codes encoded by a frame unitfrom the memory card 319 serially. The picture expansion circuit 320decodes the luminance signal Y and the color-difference signals U, V bya frame unit to output to the read signal processing circuit 321.

In cases of FIGS. 57 and 58, signals are encoded or decoded by a frameunit. Signals can be encoded or decoded by a certain size of block otherthan a frame unit. Further, it is possible to encode or decode by aplurality of lines.

FIG. 59 shows another configuration of the digital camera 600.

Different from FIG. 53, the digital camera shown in FIG. 59 displays thepicture on the monitor 324 through the frame memory 316.

FIG. 60 shows yet another configuration of the digital camera 600.

Different from FIG. 53, the digital camera shown in FIG. 60 does notinclude the memory card 319 and the picture compression circuit 318 andthe picture expansion circuit 320 are located before and after the framememory 316, respectively in the digital camera.

In both cases of FIGS. 59 and 60, the picture compression circuit 318and the picture expansion circuit 320 shown in FIGS. 55 through 58 canbe used.

FIG. 61 shows another configuration of the digital camera 600 and thecomputer 700.

It is characteristic point of the configuration shown in FIG. 61 thatthe picture compression circuit 318 of the digital camera 600 implementscompression process and the computer 700 implements expansion process.In the digital camera 600, only compression is implemented and thecompressed data is stored in the memory card 319. The memory card 319 iscoupled to the computer 700 off-line. A CPU (Central Processing Unit)701 and a picture expansion program 703 stored in a RAM (Random AccessMemory) 702 read the code stored in the memory card 319 and expands theread code. Then, required processing of the picture is performed by apicture processing program 704 and the picture can be displayed orprinted out. If communication function is provided to the digital camera600, the code stored in the memory card 319 can be transmit to a distantplace through wired communication or wireless communication.

FIGS. 62 and 63 show cases where the picture compression circuit 318inputs the color signals R, G, and B.

FIGS. 64 and 65 show cases where the picture compression circuit 318inputs the color signals R, G1, G2 and B.

The picture expansion circuit 320 decodes the color signal by aconfiguration similar to the configurations of FIGS. 62 through 65,which is not shown in the figure.

In the aforementioned embodiments, the case where the codes areaccumulated by the memory card 319 is explained. Secondary storagedevice such as a flexible disk, a harddisk, a flash memory can beapplied instead of the memory card 319. In another way, the code is notstored in the storage device,but transmitted to the outside by acommunication apparatus or cable and so on.

INDUSTRIAL APPLICABILITY

As described above, the present invention provides an efficient encodingapparatus, an efficient decoding apparatus, an efficient encodingmethod, and an efficient decoding method. More specifically, accordingto the present invention, picture information is encoded or decodedefficiently in accordance with the encoding methods corresponding to aplurality of encoding modes.

According to the present invention, picture information can beappropriately encoded and correctly decoded even if a code is notdetermined at the time of switching between a plurality of encodingmodes.

According to the present invention, even when the interpretation of theMPS and the LPS has been changed, appropriate encoding and correctdecoding can be implemented.

According to the present invention, the encoding apparatus or thedecoding apparatus can be constructed in a compact size.

Further, according to the invention, higher compressionability can beobtained than conventional picture compressionability, thus the picturewith higher quality can be stored in smaller recording capacity of therecording medium.

Accordingly, a larger amount of picture information can be stored in therecording medium provided to the picture processing apparatus such as adigital camera than the conventional picture processing apparatus.

In view of these advantages, the present invention has sufficientindustrial applicability.

The invention being thus described, it will be obvious that the same maybe regarded as departure from the spirit and scope of the invention, andall such modifications as would be obvious to one skilled in the art areintended to be included within the scope of the following claims.

What is claimed is:
 1. An encoding apparatus comprising: a pictureelement memory for receiving and storing a picture element having avalue within a predetermined range as an encoding picture element, andfor outputting a value of an encoded picture element adjacent to theencoding picture element as the value of a reference picture element; amode determinator for selecting one of a specific encoding mode and anencoding mode other than the specific encoding mode from a plurality ofpredefined encoding modes for the encoding picture element based on thevalue of the reference picture element; a first encoding section forpredicting the value of the encoding picture element, determiningwhether the prediction is correct, encoding the value of the encodingpicture element based on a result of the determination, and foroutputting a codeword for the encoding picture element; a secondencoding section for predicting the value of the encoding pictureelement, encoding the value of the encoding picture element, and foroutputting a codeword for the encoding picture element; and an encodingcontroller for selectively operating said first encoding section andsaid second encoding section based on a selected result of said modedeterminator, wherein said first encoding section comprises: a firstpredictor for calculating a prediction value of the encoding pictureelement based on the value of the reference picture element; a firstprediction error calculator for calculating an error between the valueof the encoding picture element and the prediction value calculated bysaid first predictor as a prediction error; a determinator fordetermining whether the prediction error calculated by said firstprediction error calculator is a specific value, and for outputting aresult of the determination; a first encoder for receiving and encodingthe result of the determination output from said determinator, and foroutputting the codeword for the encoding picture element to be encodedin the selected specific encoding mode; and a second encoder forencoding the prediction error calculated by said first prediction errorcalculator when the prediction error is other than the specific valuefor the encoding picture element to be encoded in the selected specificencoding mode, and for outputting the codeword for the encoding pictureelement to be encoded in the selected specific encoding mode; whereinthe mode determinator receives the value of the reference pictureelement output from said picture element memory and the result of thedetermination output from said determinator, and selects the encodingmode based on the value of the reference picture element and the resultsof the determination.
 2. The encoding apparatus as claimed in claim 1,wherein said second encoding section comprises: a second predictor forcalculating a prediction value of the encoding picture element based onthe value of the reference picture element; a second prediction errorcalculator for calculating an error between the value of the encodingpicture element and the prediction value calculated by said secondpredictor as a prediction error; and a third encoder for encoding theprediction error calculated by said second prediction error calculatorfor the encoding picture element to be encoded in the selected encodingmode other than the specific encoding mode, regardless of whether theprediction error is the specific value, and for outputting the codewordfor the encoding picture element to be encoded in the selected encodingmode other than the specific encoding mode.
 3. The encoding apparatusaccording to claim 1, wherein the second encoding section comprises: asecond predictor for calculating a prediction value of the encodingpicture element based on the value of the reference picture element; asecond prediction error calculator for calculating an error between thevalue of the encoding picture element and the prediction valuecalculated by said second predictor as a prediction error; and a thirdencoder for encoding the prediction error calculated by said secondprediction error calculator for the encoding picture element to beencoded in the selected encoding mode other than the specific encodingmode, regardless of whether the prediction error is the specific value,and for outputting the codeword for the encoding picture element to beencoded in the selected encoding mode other than the specific encodingmode, wherein the first encoder comprises a first probability estimatorfor receiving the result of the determination output from thedeterminator as a sequence of binary symbols and estimating anoccurrence probability of one of the binary symbols, and a firstcodeword allotter for encoding the sequence of binary symbols, whereinthe second encoder comprises a first error-to-symbol converter forreceiving the prediction error and converting the prediction error intoa sequence of binary symbols, a second probability estimator forreceiving the sequence of binary symbols and estimating an occurrenceprobability of one of the binary symbols, and a second codeword allotterfor encoding the sequence of binary symbols; and wherein the thirdencoder comprises a second error-to-symbol converter for receiving theprediction error and converting the prediction error into a sequence ofbinary symbols, a third probability estimator for receiving the sequenceof binary symbols and estimating an occurrence probability of one of thebinary symbols, and a third codeword allotter for encoding the sequenceof binary symbols, and wherein the encoding controller has a codewordtransmission order controller for changing an order for outputtingcodewords when a codeword has been determined by at least one of thefirst encoder, the second encoder, and the third encoder and when acodeword has not been determined by the other encoders.
 4. The encodingapparatus as claimed in claim 3, wherein at least one of the firstcodeword allotter , the second codeword allotter and the third codewordallotter changes interpretation as to which one of the binary symbols isa more probable symbol, based on a change in probability estimation forone of the binary symbols respectively implemented by the firstprobability estimator for the first codeword allotter, the secondprobability estimator for the second codeword allotter, and the thirdprobability estimator for the third codeword allotter.
 5. The encodingapparatus as claimed in claim 3, wherein the first predictor of thefirst encoding section and the second predictor of the second encodingsection are combined into a predictor.
 6. The encoding apparatus asclaimed in claim 3, wherein at least two encoders of the first encoder,the second encoder, and the third encoder are combined into an encoder.7. The encoding apparatus as claimed in claim 1, wherein the encodingapparatus is provided in a semiconductor chip.
 8. The encoding apparatusas claimed in claim 1, wherein the encoding apparatus is provided in acircuit board.
 9. An encoding apparatus, comprising: a picture elementmemory for receiving and storing a picture element having a value withina predetermined range as an encoding picture element, and for outputtinga value of an encoded picture element adjacent to the encoding pictureelement as the value of a reference picture element; a mode determinatorfor selecting one of a specific encoding mode and an encoding mode otherthan the specific encoding mode from a plurality of predefined encodingmodes for the encoding picture element based on the value of thereference picture element; a first encoding section for predicting thevalue of the encoding picture element, determining whether theprediction is correct, encoding the value of the encoding pictureelement based on a result of the determination, and for outputting acodeword for the encoding picture element; a second encoding section forpredicting the value of the encoding picture element, encoding the valueof the encoding picture element, and for outputting a codeword for theencoding picture element; and an encoding controller for selectivelyoperating said first encoding section and said second encoding sectionbased on a selected result of said mode determinator, and wherein saidfirst encoding section comprises: a first predictor for calculating aprediction value of the encoding picture element based on the value ofthe reference picture element; a first prediction error calculator forcalculating an error between the value of the encoding picture elementand the prediction value calculated by said first predictor as aprediction error; a determinator for determining whether the predictionerror calculated by said first prediction error calculator is a specificvalue, and for outputting a result of the determination; a first encoderfor receiving and encoding the result of the determination output fromsaid determinator, and for outputting the codeword for the encodingpicture element to be encoded in the selected specific encoding mode;and a second encoder for encoding the prediction error calculated bysaid first prediction error calculator when the prediction error isother than the specific value for the encoding picture element to beencoded in the selected specific encoding mode, and for outputting thecodeword for the encoding picture element to be encoded in the selectedspecific encoding mode, wherein based on information as to which one ofthe binary symbols is a more probable symbol and an estimated occurrenceprobability of the more probable symbol, at least one of the firstencoder and the second encoder implements encoding for an extendedinformation source of the binary symbols effected by selecting a codemost suited to a state of the extended information source of the binarysymbols assumed from the estimated occurrence probability of the moreprobable symbol from a set of Huffman codes prepared systematically forthe extended information source of the binary symbols.
 10. The encodingapparatus as claimed in claim 9, wherein the first predictor of thefirst encoding section and the second predictor of the second encodingsection are combined into a predictor.
 11. The encoding apparatus asclaimed in claim 9, wherein at least two encoders of the first encoder,the second encoder, and the third encoder are combined into an encoder.12. A picture processing apparatus for receiving picture signalsrepresenting picture elements, encoding the picture elements representedby the picture signals into codes by using the encoding apparatusaccording to claim 9, and for outputting the codes to a subsequentprocessing apparatus.
 13. The picture processing apparatus according toclaim 12, further comprising: a picture pick-up device for picking up apicture composed of a plurality of picture elements; a picturecompression circuit for compressing the picked-up picture; and a memoryfor storing the compressed picture, wherein the picture compressioncircuit comprises the encoding apparatus.
 14. The picture processingapparatus as claimed in claim 13, wherein the second encoding sectioncomprises: a second predictor for calculating a prediction value of theencoding picture element based on the value of the reference pictureelement; a second prediction error calculator for calculating an errorbetween the value of the encoding picture element and the predictionvalue calculated by the second predictor as a prediction error.
 15. Thepicture processing apparatus according to claim 13, further comprising:a picture pick-up device for picking up a picture composed of aplurality of picture elements; a picture compression circuit forcompressing the picked up picture; a memory for storing the compressedpicture; and a picture expansion circuit for expanding the storedpicture, wherein the picture expansion circuit comprises the decodingapparatus.
 16. The picture processing apparatus as claimed in claim 5,wherein the second decoding section comprises: a second predictor forcalculating a prediction value of the decoding picture element based onthe value of the reference picture element; a third decoder for decodingthe codeword for the decoding picture element to be decoded in theselected decoding mode other than the specific decoding mode into theprediction error regardless of whether the prediction error is thepredetermined value; a second decoding picture element calculator forcalculating the value of the decoding picture element to be decoded inthe selected decoding mode other than the specific decoding mode basedon the prediction value of the decoding picture element calculated bythe second predictor and the prediction error obtained by the thirddecoder.
 17. A decoding apparatus, comprising: a picture element memoryfor storing decoded picture elements having values within apredetermined range, and outputting the value of one of the decodedpicture elements adjacent to a decoding picture element as a value of areference picture element; a mode determinator for selecting one of aspecific decoding mode and a decoding mode other than the specificdecoding mode from a plurality of predefined decoding modes for thedecoding picture element based on the value of the reference pictureelement; a first decoding section for receiving a codeword, predicting avalue of the decoding picture element, determining whether theprediction is correct, and for decoding the codeword into the value ofthe decoding picture element based on a result of the determination; asecond decoding section for receiving a codeword for the decodingpicture element, predicting the value of the decoding picture element,decoding the codeword; and a decoding controller for selectivelyoperating said first decoding section and said second decoding sectionbased on a selected result of said mode determinator; wherein said firstdecoding section comprises: a first predictor for calculating aprediction value of the decoding picture element based on the value ofthe reference picture element; a first decoder for decoding the codewordfor the decoding picture element to be decoded in the selected specificdecoding mode into a result of determination indicating whether aprediction error is a predetermined value; a second decoder for decodingthe codeword for the decoding picture element to be decoded in theselected specific decoding mode and having the prediction error otherthan the predetermined value into the prediction error other than thepredetermined value; and a first decoding picture element calculator forcalculating the value of the decoding picture element based on theprediction value of the decoding picture element calculated by saidfirst predictor, the result of the determination, and the predictionerror obtained by said second decoder; wherein the mode determinatorreceives the value of the reference picture element output from saidpicture element memory and the result of the determination output fromsaid first decoder, and selects the decoding mode based on the value ofthe reference picture element and the result of the determination. 18.The decoding apparatus as claimed in claim 17, wherein said seconddecoding section comprises: a second predictor for calculating aprediction value of the decoding picture element based on the value ofthe reference picture element; a third decoder for decoding the codewordfor the decoding picture element to be decoded in the selected decodingmode other than the specific decoding mode into the prediction errorregardless of whether the prediction error is the predetermined value;and a second decoding picture element calculator for calculating thevalue of the decoding picture element to be decoded in the selecteddecoding mode other than the specific decoding mode based on theprediction value of the decoding picture element calculated by saidsecond predictor and the prediction error obtained by said thirddecoder.
 19. The decoding apparatus as claimed in claim 17, wherein thesecond decoding section comprises: a second predictor for calculating aprediction value of the decoding picture element based on the value ofthe reference picture element; a third decoder for decoding the codewordfor the decoding picture element to be decoded in the selected decodingmode other than the specific decoding mode into the prediction errorregardless of whether the prediction error is the predetermined value; asecond decoding picture element calculator for calculating the value ofthe decoding picture element to be decoded in the selected decoding modeother than the specific decoding mode based on the prediction value ofthe decoding picture element calculated by said second predictor and theprediction error obtained by said third decoder; wherein said firstdecoder has a first symbol restoring device for receiving the codewordand decoding the codeword into a sequence of binary symbols and a firstprobability estimator for estimating an occurrence probability of one ofthe binary symbols, and wherein said first decoder outputs one of thebinary symbols as a result of determination, wherein said second decoderhas a second symbol restoring device for receiving the codeword anddecoding the codeword into a sequence of binary symbols, a secondprobability estimator for receiving the binary symbols and estimating anoccurrence probability of one of the binary symbols, and a firstsymbol-to-error converter for receiving the sequence of binary symbolsand converting the sequence of binary symbols into the prediction error,wherein said third decoder has a third symbol restoring device forreceiving the codeword and decoding the codeword into a sequence ofbinary symbols, a third probability estimator for receiving the binarysymbols and estimating an occurrence probability of one of the binarysymbols, and a second symbol-to-error converter for receiving thesequence of binary symbols and converting the sequence of binary symbolsinto the prediction error; and wherein the decoding controller has abinary-symbol sequence using order controller for changing an order ofusing decoded binary symbols in a case where, before all sequences ofbinary symbols decoded by at least one of the first decoder, the seconddecoder, and the third decoder are used up, a sequence of binary symbolsis output from the other one of the first decoder, the second decoder,and the third decoder.
 20. The decoding apparatus as claimed in claim19, wherein at least one of the first symbol restoring device, thesecond symbol restoring device, and the third symbol restoring devicechanges interpretation as to which one of the binary symbols is a moreprobable symbol based on a change in probability estimation for thebinary symbols respectively implemented by the first probabilityestimator for the first symbol restoring device, the second probabilityestimator for the second symbol restoring device and the thirdprobability estimator for the third symbol restoring device.
 21. Thedecoding apparatus as claimed in claim 19, wherein the first predictorof the first decoding section and the second predictor of the seconddecoding section are combined into a predictor.
 22. The decodingapparatus as claimed in claim 19, wherein at least two decoders of thefirst decoder, the second decoder, and the third decoder are combinedinto a decoder.
 23. A decoding apparatus, comprising: a picture elementmemory for storing decoded picture elements having values within apredetermined range, and outputting the value of one of the decodedpicture elements adjacent to a decoding picture element as a value of areference picture element; a mode determinator for selecting one of aspecific decoding mode and a decoding mode other than the specificdecoding mode from a plurality of predefined decoding modes for thedecoding picture element based on the value of the reference pictureelement; a first decoding section for receiving a codeword, predicting avalue of the decoding picture element, determining whether theprediction is correct, and for decoding the codeword into the value ofthe decoding picture element based on a result of the determination; asecond decoding section for receiving a codeword for the decodingpicture element, predicting the value of the decoding picture element,and decoding the codeword; and a decoding controller for selectivelyoperating said first decoding section and said second decoding sectionbased on a selected result of said mode determinator, and wherein saidfirst decoding section comprises: a first predictor for calculating aprediction value of the decoding picture element based on the value ofthe reference picture element; a first decoder for decoding the codewordfor the decoding picture element to be decoded in the selected specificdecoding mode into a result of determination indicating whether aprediction error is predetermined value; a second decoder for decodingthe codeword for the decoding picture element to be decoded in theselected specific decoding mode and having the prediction error otherthan the predetermined value into the prediction error other than thepredetermined value; and a first decoding picture element calculator forcalculating the value of the decoding picture element based on theprediction value of the decoding picture element calculated by saidfirst predictor, the result of the determination, and the predictionerror obtained by said second decoder, wherein based on information asto which one of the binary symbols is a more probable symbol and anestimated occurrence probability of the more probable symbol, at leastone of the first decoder and the second decoder implements decoding foran extended information source of binary symbols effected by selecting acode most suited to a state of the extended information source of binarysymbols assumed from the estimated occurrence probability of the moreprobable symbol from a set of Huffman codes prepared systematically forthe extended information source of binary symbols.
 24. The decodingapparatus as claimed in claim 23, wherein the first predictor of thefirst decoding section and the second predictor of the second decodingsection are combined into a predictor.
 25. The decoding apparatus asclaimed in claim 23, wherein at least two decoders of the first decoder,the second decoder, and the third decoder are combined into a decoder.26. A picture processing apparatus for receiving a picture signalrepresenting a code for a picture element, decoding the code into thevalue of the picture element by the decoding apparatus according toclaim 23, and for outputting the picture element to a subsequentprocessing apparatus.
 27. An encoding method comprising: an outputtingstep of receiving and storing a picture element having a value within apredetermined range as an encoding picture element, and outputting avalue of an encoded picture element adjacent to the encoding pictureelement as the value of a reference picture element; a mode decidingstep of selecting one of a specific encoding mode and an encoding modeother than the specific encoding mode from a plurality of predefinedencoding modes for the encoding picture element based on the value ofthe reference picture element; a first main encoding step of predictingthe value of the encoding picture element, determining whether theprediction is correct, encoding the value of the encoding pictureelement based on a result of determination, and outputting a codewordfor the encoding picture element; a second main encoding step ofpredicting the value of the encoding picture element, encoding the valueof the encoding picture element, and outputting a codeword for theencoding picture element; and an encoding controlling step ofselectively operating said first main encoding step and said second mainencoding step based on a selected result of said mode deciding step;wherein said first main encoding step comprises: a first predicting stepof calculating a prediction value of the encoding picture element basedon the value of the reference picture element; a first prediction errorcalculating step of calculating an error between the value of theencoding picture element and the prediction value calculated by saidfirst predicting step as a prediction error; a determination step ofdeterminating whether the prediction error calculated by said firstprediction error calculating step is a predetermined value, andoutputting a result of the determination; a first encoding step ofreceiving and encoding the result of the determination output by saiddetermination step and outputting the codeword for the encoding pictureelement to be encoded in the selected specific encoding mode; and asecond encoding step of encoding the prediction error calculated by saidfirst prediction error calculating step when the prediction error isother than the predetermined value for the encoding picture element tobe encoded in the selected specific encoding mode, and outputting thecodeword for the encoding picture element to be encoded in the selectedspecific encoding mode; wherein the mode deciding step receives thevalue of the reference picture element output from said outputting stepand the result of the determination output from said determination step,and selects the encoding mode based on the value of the referencepicture element and the result of the determination.
 28. The encodingmethod as claimed in claim 27, wherein said second main encoding stepcomprises: a second predicting step of calculating a prediction value ofthe encoding picture element based on the value of the reference pictureelement; a second prediction error calculating step of calculating anerror between the value of the encoding picture element and theprediction value calculated by said second predicting step as aprediction error; and a third encoding step of encoding the predictionerror calculated by said second prediction error calculating step forthe encoding picture element to be encoded in the selected encoding modeother than the specific encoding mode, regardless of whether theprediction error is the predetermined value, and outputting the codewordfor the encoding picture element to be encoded in the selected encodingmode other than the specific encoding mode.
 29. The encoding methodaccording to claim 27, wherein the second main encoding step comprises:a second predicting step of calculating a prediction value of theencoding picture element based on the value of the reference pictureelement; a second prediction error calculating step of calculating anerror between the value of the encoding picture element and theprediction value calculated by the second predicting step as aprediction error; and a third encoding step of encoding the predictionerror calculated by the second prediction error calculating step for theencoding picture element to be encoded in the selected encoding modeother than the specific encoding mode, regardless of whether theprediction error is the predetermined value, and outputting the codewordfor the encoding picture element to be encoded in the selected encodingmode other than the specific encoding mode; wherein the first encodingstep comprises a first probability estimating step of receiving theresult of the determination output by the determination step as asequence of binary symbols and estimating an occurrence probability ofone of the binary symbols and a first codeword allotting step ofencoding the sequence of binary symbols, wherein the second encodingstep comprises a first error-to-symbol converting step of receiving theprediction error and converting the prediction error into a sequence ofbinary symbols, a second probability estimating step of receiving thesequence of binary symbols and estimating an occurrence probability ofone of the binary symbols, and a second codeword allotting step ofencoding the sequence of binary symbols, and wherein the third encodingstep comprises a second error-to-symbol converting step of receiving theprediction error and converting the prediction error into a sequence ofbinary symbols, a third probability estimating step of receiving thesequence of binary symbols and estimating an occurrence probability ofone of the binary symbols, and a third codeword allotting step ofencoding the sequence of binary symbols, and wherein based oninformation as to which one of the binary symbols is a more probablesymbol and an estimated occurrence probability of the more probablesymbol, at least one of the first codeword allotting step, the secondcodeword allotting step, and the third codeword allotting stepimplements encoding for an extended information source of the binarysymbols effected by selecting a codeword table most suited to a state ofthe extended information source of the binary symbols assumed from theestimated occurrence probability of the more probable symbol from a setof Huffman codeword tables prepared systematically for the extendedinformation source of the binary symbols.
 30. An encoding method,comprising: an outputting step of receiving and storing a pictureelement having a value within a predetermined range as an encodingpicture element, and outputting a value of an encoded picture elementadjacent to the encoding picture element as the value of a referencepicture element; a mode deciding step of selecting one of a specificencoding mode and an encoding mode other than the specific encoding modefrom a plurality of predefined encoding modes for the encoding pictureelement based on the value of the reference picture element; a firstmain encoding step of predicting the value of the encoding pictureelement, determining whether the prediction is correct, encoding thevalue of the encoding picture element based on a result ofdetermination, and outputting a codeword for the encoding pictureelement; a second main encoding step of predicting the value of theencoding picture element, encoding the value of the encoding pictureelement, and outputting a codeword for the encoding picture element; andan encoding controlling step of selectively operating said first mainencoding step and said second main encoding step based on a selectedresult of said mode deciding step, and wherein said first main encodingstep comprises: a first predicting step of calculating a predictionvalue of the encoding picture element based on the value of thereference picture element; a first prediction error calculating step ofcalculating an error between the value of the encoding picture elementand the prediction value calculated by said first predicting step as aprediction error; a determination step of determining whether theprediction error calculated by said first prediction error calculatingstep is a predetermined value, and outputting a result of thedetermination; a first encoding step of receiving and encoding theresult of the determination output by said determination step andoutputting the codeword for the encoding picture element to be encodedin the selected specific encoding mode; and a second encoding step ofencoding the prediction error calculated by said first prediction errorcalculating step when the prediction error is other than thepredetermined value for the encoding picture element to be encoded inthe selected specific encoding mode, and outputting the codeword for theencoding picture element to be encoded in the selected specific encodingmode; wherein based on information as to which one of the binary symbolsis a more probable symbol and an estimated occurrence probability of themore probable symbol, at least one of the first encoding step and thesecond encoding step implements encoding for an extended informationsource of the binary symbols effected by selecting a code most suited toa state of the extended information source of the binary symbols assumedfrom the estimated occurrence probability of the more probable symbolfrom a set of Huffman codes prepared systematically for the extendedinformation source of the binary symbols.
 31. A decoding method,comprising: an outputting step of storing decoded picture elementshaving values within a predetermined range, and outputting the value ofone of the decoded picture elements adjacent to a decoding pictureelement as the value of a reference picture element; a mode decidingstep of selecting one of a specific decoding mode and a decoding modeother than the specific decoding mode from a plurality of predefineddecoding modes for the decoding picture element based on the value ofthe reference picture element; a first main decoding step of receiving acodeword, predicting a value of the decoding picture element,determining whether the prediction is correct, and decoding the codewordinto the value of the decoding picture element based on a result of thedetermination; a second main decoding step of receiving a codeword,predicting the value of the decoding picture element, and decoding thecodeword into the value of the decoding picture element; and a decodingcontrolling step of selectively operating said first main decoding stepand said second main decoding step based on a selected result of saidmode deciding step; wherein said first main decoding step comprises: afirst predicting step of calculating a prediction value of the decodingpicture element based on the value of the reference picture element; afirst decoding step of decoding the codeword for the decoding pictureelement to be decoded in the selected specific decoding mode into aresult of determination indicating whether a prediction error is apredetermined value; a second decoding step of decoding the codeword forthe decoding picture element to be decoded in the selected specificdecoding mode and having the prediction error other than thepredetermined value into the prediction error other than thepredetermined value; and a first decoding picture element calculatingstep of calculating the value of the decoding picture element based onthe prediction value for the decoding picture element calculated by saidfirst predicting step, the result of the determination, and theprediction error other than the predetermined value obtained by saidsecond decoding step; wherein the mode deciding step receives the valueof the reference picture element output from said outputting step andthe result of the determination output from said first decoding step,and selects the decoding mode based on the value of the referencepicture element and the result of the determination.
 32. The decodingmethod as claimed in claim 31, wherein said second main decoding stepcomprises: a second predicting step of calculating a prediction value ofthe decoding picture element based on the value of the reference pictureelement; a third decoding step of decoding the codeword for the decodingpicture element to be decoded in the selected decoding mode other thanthe specific decoding mode into a prediction error regardless of whetherthe prediction error is the predetermined value; and a second decodingpicture element calculating step of calculating the value of thedecoding picture element to be decoded in the selected decoding modeother than the specific decoding mode based on the prediction valuecalculated by said second predicting step and the prediction errorcalculated by said third decoding step.
 33. The decoding methodaccording to claim 31, wherein the second main decoding step comprises:a second predicting step of calculating a prediction value of thedecoding picture element based on the value of the reference pictureelement; a third decoding step of decoding the codeword for the decodingpicture element to be decoded in the selected decoding mode other thanthe specific decoding mode into a prediction error regardless of whetherthe prediction error is the predetermined value; and a second decodingpicture element calculating step of calculating the value of thedecoding picture element to be decoded in the selected decoding modeother than the specific decoding mode based on the prediction valuecalculated by the second predicting step and the prediction errorcalculated by the third decoding step, wherein the first decoding stepcomprises a first symbol restoring step for receiving the codeword anddecoding the codeword into a sequence of binary symbols and a firstprobability estimating step of estimating an occurrence probability ofone of the binary symbols, and a step of outputting one of the binarysymbols as a result of the determination, wherein the second decodingstep comprises a second symbol restoring step of receiving the codewordand decoding the codeword into a sequence of binary symbols, a secondprobability estimating step of estimating an occurrence probability ofone of the binary symbols, and a first symbol-to-error converting stepof receiving the sequence of binary symbols and converting the sequenceof binary symbols into the prediction error, and wherein the thirddecoding step comprises a third symbol restoring step of receiving thecodeword and decoding the codeword into a sequence of binary symbols, athird probability estimating step of receiving the binary symbols andestimating an occurrence probability of one of the binary symbols, and asecond symbol-to-error converting step of receiving the sequence ofbinary symbols and converting the sequence of binary symbols into theprediction error, and wherein at least one of the first symbol restoringstep, the second symbol restoring step, and the third symbol restoringstep includes a step of changing interpretation as to which one of thebinary symbols is a more probable symbol based on a change inprobability estimation for the binary symbols respectively implementedby the first probability estimating step for the first symbol restoringstep, the second probability estimating step for the second symbolrestoring step, and the third probability estimating step for the thirdsymbol restoring step.
 34. A decoding method, comprising: an outputtingstep of storing decoded picture elements having values within apredetermined range, and outputting the value of one of the decodedpicture elements adjacent to a decoding picture element as the value ofa reference picture element; a mode deciding step of selecting one of aspecific decoding mode and a decoding mode other than the specificdecoding mode from a plurality of predefined decoding modes for thedecoding picture element based on the value of the reference pictureelement; a first main decoding step of receiving a codeword, predictinga value of the decoding picture element, determining whether theprediction is correct, and decoding the codeword into the value of thedecoding picture element based on a result of the determination; asecond main decoding step of receiving a codeword, predicting the valueof the decoding picture element, and decoding the codeword into thevalue of the decoding picture element; and a decoding controlling stepof selectively operating said first main decoding step and said secondmain decoding step based on a selected result of said mode decidingstep, and wherein said first main decoding step comprises: a firstpredicting step of calculating a prediction value of the decodingpicture element based on the value of the reference picture element; afirst decoding step of decoding the codeword for the decoding pictureelement to be decoded in the selected specific decoding mode into aresult of determination indicating whether a prediction error is apredetermined value; a second decoding step of decoding the codeword forthe decoding picture element to be decoded in the selected specificdecoding mode and having the prediction error other than thepredetermined value into the prediction error other than thepredetermined value; and a first decoding picture element calculatingstep of calculating the value of the decoding picture element based onthe prediction value for the decoding picture element calculated by saidfirst predicting step, the result of the determination, and theprediction error other than the predetermined value obtained by saidsecond decoding step, and wherein said second main decoding stepcomprises: a second predicting step of calculating a prediction value ofthe decoding picture element based on the value of the reference pictureelement; a third decoding step of decoding the codeword for the decodingpicture element to be decoded in the selected decoding mode other thanthe specific decoding mode into a prediction error regardless of whetherthe prediction error is the predetermined value; and a second decodingpicture element calculating step of calculating the value of thedecoding picture element to be decoded in the selected decoding modeother than the specific decoding mode based on the prediction valuecalculated by said second predicting step and the prediction errorcalculated by said third decoding step, wherein said first decoding stepcomprises a first symbol restoring step for receiving the codeword anddecoding the codeword into a sequence of binary symbols and a firstprobability estimating step of estimating an occurrence probability ofone of the binary symbols, and a step of outputting one of the binarysymbols as a result of the determination, wherein said second decodingstep comprises a second symbol restoring step of receiving the codewordand decoding the codeword into a sequence of binary symbols, a secondprobability estimating step of estimating an occurrence probability ofone of the binary symbols, and a first symbol-to-error converting stepof receiving the sequence of binary symbols and converting the sequenceof binary symbols into the prediction error, wherein said third decodingstep comprises a third symbol restoring step of receiving the codewordand decoding the codeword into a sequence of binary symbols, a thirdprobability estimating step of receiving the binary symbols andestimating an occurrence probability of one of the binary symbols, and asecond symbol-to-error converting step of receiving the sequence ofbinary symbols and converting the sequence of binary symbols into theprediction error, and wherein at least one of said first symbolrestoring step, said second symbol restoring step, and said third symbolrestoring step includes a step of changing interpretation as to whichone of the binary symbols is a more probable symbol based on a change inprobability estimation for the binary symbols respectively implementedby said first probability estimating step for said first symbolrestoring step, said second probability estimating step for said secondsymbol restoring step, and said third probability estimating step forsaid third symbol restoring step; wherein based on information as towhich one of the binary symbols is a more probable symbol and anestimated occurrence probability of the more probable symbol, at leastone of the first symbol restoring step, the second symbol restoringstep, and the third symbol restoring step implements decoding for anextended information source of binary symbols effected by selecting acode most suited to a state of the extended information source of binarysymbols assumed from the estimated occurrence probability of the moreprobable symbol from a set of Huffman codes prepared systematically forthe extended information source of binary symbols.
 35. A pictureprocessing apparatus for receiving picture signals representing pictureelements, encoding the picture elements represented by the picturesignals into codes by using an encoding apparatus therein, and foroutputting the codes to a subsequent processing apparatus, the encodingapparatus comprising: a picture element memory for receiving and storinga picture element having a value within a predetermined range as anencoding picture element, and for outputting a value of an encodedpicture element adjacent to the encoding picture element as the value ofa reference picture element; a mode determinator for selecting one of aspecific encoding mode and an encoding mode other than the specificencoding mode from a plurality of predefined encoding modes for theencoding picture element based on the value of the reference pictureelement; a first encoding section for predicting the value of theencoding picture element, determining whether the prediction is correct,encoding the value of the encoding picture element based on a result ofthe determination, and for outputting a codeword for the encodingpicture element; a second encoding section for predicting the value ofthe encoding picture element, encoding the value of the encoding pictureelement, and for outputting a codeword for the encoding picture element;and an encoding controller for selectively operating said first encodingsection and said second encoding section based on a selected result ofsaid mode determinator; wherein the first encoding section comprises: afirst predictor for calculating a prediction value of the encodingpicture element based on the value of the reference picture element; afirst prediction error calculator for calculating an error between thevalue of the encoding picture element and the prediction valuecalculated by the first predictor as a prediction error; a determinatorfor determinating whether the prediction error calculated by the firstprediction error calculator is a specific value, and for outputting aresult of the determination; a first encoder for receiving and encodingthe result of the determination output from the determinator, and foroutputting the code word for the encoding picture element to be encodedin the selected specific encoding mode; and a second encoder forencoding the prediction error calculated by the first prediction errorcalculator when the prediction error is other than the specific valuefor the encoding picture element to be encoded in the selected specificencoding mode, and for outputting the codeword for the encoding pictureelement to be encoded in the selected specific encoding mode, whereinthe mode determinator receives the value of the reference pictureelement output from said picture element memory and the result of thedetermination output from said determinator, and selects the encodingmode based on the value of the reference picture element and the resultsof the determination.
 36. The picture processing apparatus as claimed inclaim 35, wherein the picture processing apparatus is a computer. 37.The picture processing apparatus as claimed in claim 35, wherein thepicture processing apparatus is a scanner.
 38. The picture processingapparatus as claimed in claim 35, wherein the picture processingapparatus is a facsimile machine.
 39. The picture processing apparatusas claimed in claim 35, wherein the picture processing apparatus is adisplay unit.
 40. The picture processing apparatus as claimed in claim35, wherein the picture processing apparatus is a storage device. 41.The decoding apparatus as claimed in claim 35, wherein the decodingapparatus is provided in a semiconductor chip.
 42. The decodingapparatus as claimed in claim 35, wherein the decoding apparatus isprovided in a circuit board.
 43. The picture processing apparatus asclaimed in claim 35, wherein said mode determinator selects an encodingmode for an encoding picture element based on an encoding mode for anencoded picture element preceding the encoding picture element.
 44. Thepicture processing apparatus claimed in claim 35, further comprising: apicture pick-up device for picking up a picture composed of a pluralityof picture elements; a picture compression circuit for compressing thepicked-up picture; and a memory for storing the compressed picture,wherein said picture compression circuit includes an encoding apparatus.45. A picture processing apparatus comprising: a picture pick-up devicefor picking up a picture composed of a plurality of picture elements; apicture compression circuit for compressing the picked-up picture; and amemory for storing the compressed picture, wherein said picturecompression circuit includes an encoding apparatus comprising: a pictureelement memory for receiving and storing a picture element having avalue within a predetermined range as an encoding picture element, andfor outputting a value of an encoded picture element adjacent to theencoding picture element as the value of a reference picture element; anencoding section for predicting the value of the encoding pictureelement, determining whether the prediction is correct, encoding thevalue of the encoding picture element based on a result of thedetermination, and for outputting a codeword for the encoding pictureelement; and an encoding controller for controlling an operation of theencoding section based on the result of the prediction made by theencoding section, wherein the encoding section comprises: a predictorfor calculating a prediction value of the encoding picture element basedon the value of the reference picture element; a prediction errorcalculator for calculating an error between the value of the encodingpicture element and the prediction value calculated by the predictor asa prediction error; a determinator for determining whether theprediction error calculated by the prediction error calculator is apredetermined value and for outputting a result of determination; afirst encoder for receiving the result of determination output from thedeterminator, encoding the result of determination, and for outputtingthe codeword; and a second encoder for encoding the prediction errorcalculated by the prediction error calculator when the prediction erroris other than the predetermined value for the encoding picture elementto be encoded and for outputting the codeword for the encoding pictureelement to be encoded, wherein based on information as to which one ofthe binary symbols is a more probable symbol and an estimated occurrenceprobability of the more probable symbol, at least one of the firstcodeword allotter and the second codeword allotter implements encodingfor an extended information source of the binary symbols effected byselecting a code most suited to a state of the extended informationsource of the binary symbols assumed from the estimated occurrenceprobability of the more probable symbol from a set of Huffman codesprepared systematically for the extended information source of thebinary symbols.
 46. The picture processing apparatus as claimed in claim45, wherein said first encoder comprises a first probability estimatorfor receiving the result of the determination output from saiddeterminator as a sequence of binary symbols and estimating anoccurrence probability of one of the binary symbols, and a firstcodeword allotter for encoding the sequence of binary symbols, whereinsaid second encoder comprises a first error-to-symbol converter forreceiving the prediction error and converting the prediction error intoa sequence of binary symbols, a second probability estimator forreceiving the sequence of binary symbols and estimating an occurrenceprobability of one of the binary symbols, and a second codeword allotterfor encoding the sequence of binary symbols, and wherein said thirdencoder comprises a second error-to-symbol converter for receiving theprediction error and converting the prediction error into a sequence ofbinary symbols, a third probability estimator for receiving the sequenceof binary symbols and estimating an occurrence probability of one of thebinary symbols, and a third codeword allotter for encoding the sequenceof binary symbols.
 47. The picture processing apparatus as claimed inclaim 46, wherein at least one of said first error-to-symbol converterand said second error-to-symbol converter successively generatescomparison values starting with a value which would most likely occur asa prediction error to be input to one of said first error-to-symbolconverter and said second error-to-symbol converter, successivelycompares the generated values with the prediction error input to one ofsaid first error-to-symbol converter and said second error-to-symbolconverter one by one, and generates and outputs a sequence of binarysymbols based on a count of comparison time until one of the generatedcomparison values coincides with the prediction error.
 48. The pictureprocessing apparatus as claimed in claim 46, wherein based oninformation as to which one of the binary symbols is a more probablesymbol and an estimated occurrence probability of the more probablesymbol, at least one of said first codeword allotter, said secondcodeword allotter, and said third codeword allotter implements encodingfor an extended information source of the binary symbols effected byselecting a codeword table most suited to a state of the extendedinformation source of the binary symbols assumed from the estimatedoccurrence probability of the more probable symbol from a set of Huffmancodeword tables prepared systematically for the extended informationsource of the binary symbols.
 49. A picture processing apparatus forreceiving a picture signal representing a code for a picture element,decoding the code into the value of the picture element by a decodingapparatus therein, and for outputting the picture element to asubsequent processing apparatus, the decoding apparatus comprising: apicture element memory for storing decoded picture elements havingvalues within a predetermined range and outputting the value of one ofthe decoded picture elements adjacent to a decoding picture element asthe value of a reference picture element; a mode determinator forselecting one of a specific decoding mode and a decoding mode other thanthe specific decoding mode from a plurality of predefined decoding modesfor the decoding picture element based on the value of the referencepicture element; a first decoding section for receiving a codeword,predicting a value of the decoding picture element, determining whetherthe prediction is correct, and for decoding the codeword into the valueof the decoding picture element based on a result of the determination;a second decoding section for receiving a codeword the decoding pictureelement, predicting the value of the decoding picture element, and fordecoding the codeword into the value of the decoding picture element;and a decoding controller for selectively operating the first decodingsection and the second decoding section based on a selected result ofsaid mode determinator; wherein said first decoding section comprises: afirst predictor for calculating a prediction value of the decodingpicture element based on the value of the reference picture element; afirst decoder for decoding the codeword for the decoding picture elementto be decoded in the selected specific decoding mode into a result ofdetermination indicating whether a prediction error is a predeterminedvalue; a second decoder for decoding the codeword for the decodingpicture element to be decoded in the selected specific decoding mode andhaving the prediction error other than the predetermined value into theprediction error other than the predetermined value; and a firstdecoding picture element calculator for calculating the value of thedecoding picture element based on the prediction value of the decodingpicture element calculated by said first predictor, the result of thedetermination, and the prediction error obtained by said second decoder;wherein the mode determinator receives the value of the referencepicture element output from said picture element memory and the resultof the determination output from said first decoder, and selects thedecoding mode based on the value of the reference picture element andthe result of the determination.
 50. The picture processing apparatus asclaimed in claim 49, wherein the picture processing apparatus is acomputer.
 51. The picture processing apparatus as claimed in claim 49,wherein the picture processing apparatus is a scanner.
 52. The pictureprocessing apparatus as claimed in claim 49, wherein the pictureprocessing apparatus is a facsimile machine.
 53. The picture processingapparatus as claimed in claim 49, wherein the picture processingapparatus is a printer.
 54. The picture processing apparatus as claimedin claim 49, wherein the picture processing apparatus is a display unit.55. The picture processing apparatus as claimed in claim 49, wherein thepicture processing apparatus is a storage device.
 56. The pictureprocessing apparatus, claimed in claim 49 further comprising: a picturepick-up device for picking up a picture composed of a plurality ofpicture elements; a picture compression circuit for compressing thepicked-up picture; a memory for storing the compressed picture; and apicture expansion circuit for expanding the stored picture, wherein saidpicture expansion circuit includes a decoding apparatus.
 57. The pictureprocessing apparatus as claimed in claim 56, wherein said seconddecoding section comprises: a second predictor for calculating aprediction value of the decoding picture element based on the value ofthe reference picture element; a third decoder for decoding the codewordfor the decoding picture element to be decoded in the selected decodingmode other than the specific decoding mode into the prediction errorregardless of whether the prediction error is the predetermined value;and a second decoding picture element calculator for calculating thevalue of the decoding picture element to be decoded in the selecteddecoding mode other than the specific decoding mode based on theprediction value of the decoding picture element calculated by saidsecond predictor and the prediction error obtained by said thirddecoder.
 58. The picture processing apparatus as claimed in claim 56,wherein said picture expansion circuit comprises a plurality of saiddecoding apparatuses for inputting an encoded luminance signal Y andencoded color-difference signals U, V in parallel and for decoding thesignals.
 59. The picture processing apparatus as claimed in claim 56,wherein said picture expansion circuit comprises a plurality of saiddecoding apparatuses for inputting encoded color signals R. G. B inparallel and for decoding the signals.
 60. The picture processingapparatus as claimed in claim 56, wherein said picture expansion circuitcomprises one decoding apparatus for serially inputting an encodedluminance signal Y and encoded color-difference signals U, V by a blockunit and for decoding the signals.
 61. The picture processing apparatusas claimed in claim 56, wherein said picture expansion circuit comprisesone decoding apparatus for serially inputting encoded color signals R,G, B by a block unit and for decoding the signals.
 62. The pictureprocessing apparatus as claimed in claim 44, wherein said secondencoding section comprises: a second predictor for calculating aprediction value of the encoding picture element based on the value ofthe reference picture element; a second prediction error calculator forcalculating an error between the value of the encoding picture elementand the prediction value calculated by said second predictor as aprediction error; and a third encoder for encoding the prediction errorcalculated by said second prediction error calculator for the encodingpicture element to be encoded in the selected encoding mode other thanthe specific encoding mode, regardless of whether the prediction erroris the specific value, and for outputting the codeword for the encodingpicture element to be encoded in the selected encoding mode other thanthe specific encoding mode.
 63. An encoding method comprising: anoutputting step of receiving and storing a picture element having avalue within a predetermined range as an encoding picture element, andoutputting a value of an encoded picture element adjacent to theencoding picture element as the value of a reference picture element; amode deciding step of selecting one of a specific encoding mode and anencoding mode other than the specific encoding mode from a plurality ofpredefined encoding modes for the encoding picture element based on thevalue of the reference picture element; a first main encoding step ofpredicting the value of the encoding picture element, determiningwhether the prediction is correct, encoding the value of the encodingpicture element based on a result of determination, and outputting acodeword for the encoding picture element; a second main encoding stepof predicting the value of the encoding picture element, encoding thevalue of the encoding picture element, and outputting a codeword for theencoding picture element; and an encoding controlling step ofselectively operating the first main encoding step and the second mainencoding step based on a selected result of the mode deciding step, andwherein the first main encoding step comprises: a first predicting stepof calculating a prediction value of the encoding picture element basedon the value of the reference picture element; a first prediction errorcalculating step of calculating an error between the value of theencoding picture element and the prediction value calculated by thefirst predicting step as a prediction error a determination step ofdeterminating whether the prediction error calculated by the firstprediction error calculating step, is a predetermined value, andoutputting a result, of the determination; a first encoding step ofreceiving and encoding the result of the determination output by thedetermination step and outputting the codeword for the encoding pictureelement to be encoded in the selected specific encoding mode; and asecond encoding step of encoding the prediction error calculated by thefirst prediction error calculating step when the prediction error isother than the predetermined value for the encoding picture element tobe encoded in the selected specific encoding mode, and outputting thecodeword for the encoding picture element to be encoded in the selectedspecific encoding mode, and wherein the second main encoding stepcomprises: a second predicting step of calculating a prediction value ofthe encoding picture element based on the value of the reference pictureelement; a second prediction error calculating step of calculating anerror between the value of the encoding picture element and theprediction value calculated by the second predicting step as aprediction error; and a third encoding step of encoding the predictionerror calculated by the second prediction error calculating step for theencoding picture element to be encoded in the selected encoding modeother than the specific encoding mode, regardless of whether theprediction error is the predetermined value, and outputting the codewordfor the encoding picture element to be encoded in the selected encodingmode other than the specific encoding mode, wherein the first encodingstep comprises a first probability estimating step of receiving theresult of the determination output by the determination step as asequence of binary symbols and estimating an occurrence probability ofone of the binary symbols and a first codeword allotting step ofencoding the sequence of binary symbols, wherein the second encodingstep comprises a first error-to-symbol converting step of receiving theprediction error and converting the prediction error into a sequence ofbinary symbols, a second probability estimating step of receiving thesequence of binary symbols and estimating an occurrence probability ofone of the binary symbols, and a second codeword allotting step ofencoding the sequence of binary symbols, and wherein the third encodingstep comprises a sec and error-to-symbol converting step of receivingthe prediction error and converting the prediction error into a sequenceof binary symbols, a third probability estimating step of receiving thesequence of binary symbols and estimating an occurrence probability ofone of the binary symbols, and a third codeword allotting step ofencoding the sequence of binary symbols, and wherein based oninformation as to which one of the binary symbols is a more probablesymbol and an estimated occurrence probability of the more probablesymbol, at least one of the first codeword allotting step, the secondcodeword allotting step, and the third codeword allotting stepimplements encoding for an extended information source of the binarysymbols effected by selecting a code most suited to a state of theextended information source of the binary symbols assumed from theestimated occurrence probability of the more probable symbol from a setof Huffman codes prepared systematically for the extended informationsource of the binary symbols.
 64. A decoding method, comprising: anoutputting step of storing decoded picture elements having values withina predetermined range, and outputting the value of one of the decodedpicture elements adjacent to a decoding picture element as the value ofa reference picture element: a mode deciding step of selecting one of aspecific decoding mode and a decoding mode other than the specificdecoding mode from a plurality of predefined decoding modes for thedecoding picture element based on the value of the reference pictureelement; a first main decoding step of receiving a code word, predictinga value of the decoding picture element, determining whether theprediction is correct, and decoding the codeword into the value of thedecoding picture element based on a result of the determination; asecond main decoding step of receiving a codeword, predicting the valueof the decoding picture element, and decoding the codeword into thevalue of the decoding picture element; and a decoding controlling stepof selectively operating the first main decoding step and the secondmain decoding step based on a selected result of the mode deciding step,wherein the first main decoding step comprises: a first predicting stepof calculating a prediction value of the decoding picture element basedon the value of the reference picture element a first decoding step ofdecoding the codeword for the decoding picture element to be decoded inthe selected specific decoding mode into a result of determinationindicating whether a prediction error is a predetermined value; a seconddecoding step of decoding the codeword for the decoding picture elementto be decoded in the selected specific decoding mode and having theprediction error other than the predetermined value into the predictionerror other than the predetermined value; and a first decoding pictureelement calculating step of calculating the value of the decodingpicture element based on the prediction value for the decoding pictureelement calculated by the first predicting step, the result of thedetermination, and the prediction error other than the predeterminedvalue obtained by the second decoding step, wherein based on informationas to which one of the binary symbols is a more probable symbol and anestimated occurrence probability of the more probable symbol, at leastone of the first decoding step and the second decoding step implementsdecoding for an extended information source of binary symbols effectedby selecting a code most suited to a state of the extended informationsource of binary symbols assumed from the estimated occurrenceprobability of the more probable symbol from a set of Huffman codesprepared systematically for the extended information source of-binarysymbols.
 65. An encoding apparatus, comprising: a picture element memoryfor receiving and storing a picture element having a value within apredetermined range as an encoding picture element, and for outputting avalue of an encoded picture element adjacent to the encoding pictureelement as the value of a reference picture element; an encoding sectionfor predicting the value of the encoding picture element, determiningwhether the prediction is correct, encoding the value of the encodingpicture element based on a result of the determination, and foroutputting a codeword for the encoding picture element; and an encodingcontroller for controlling an operation of the encoding section based onthe result of the prediction made by the encoding section, wherein theencoding section comprises: a predictor for calculating a predictionvalue of the encoding picture element based on the value of thereference picture element; a prediction error calculator for calculatingan error between the value of the encoding picture element and theprediction value calculated by the predictor as a prediction error; adeterminator for determining whether the prediction error calculated bythe prediction error calculator is a predetermined value and foroutputting a result of determination; a first encoder for receiving theresult of determination output from the determinator, encoding theresult of determination, and for outputting the codeword; and a secondencoder for encoding the prediction error calculated by the predictionerror calculator when the prediction error is other than thepredetermined value for the encoding picture element to be encoded andfor outputting the codeword for the encoding picture element to beencoded, wherein based on information as to which one of the binarysymbols is a more probable symbol and an estimated occurrenceprobability of the more probable symbol, at least one of the firstcodeword allotter and the second codeword allotter implements encodingfor an extended information source of the binary symbols effected byselecting a code most suited to a state of the extended informationsource of the binary symbols assumed from the estimated occurrenceprobability of the more probable symbol from a set of Huffman codesprepared systematically for the extended information source of thebinary symbols.
 66. A picture processing apparatus comprising: a picturepick-up device for picking up a picture composed of a plurality ofpicture elements: a picture compression circuit for compressing thepicked-up picture; and a memory for storing the compressed picture,wherein the picture compression circuit comprises the encoding apparatusaccording to claim
 65. 67. A decoding apparatus comprising: a pictureelement memory for storing decoded picture elements having values withina predetermined range and for outputting the value of one of the decodedpicture elements adjacent to a decoding picture element as the value ofa reference picture element a decoding section for receiving a codeword,predicting a value of the decoding picture element, determining whetherthe prediction is correct, and for decoding the codeword into the valueof the decoding picture element based on a result of the determination;and a decoding controller for controlling an operation of the decodingsection based on the result of the determination made by the decodingsection, wherein the decoding section comprises: a predictor forcalculating a prediction value for the decoding picture element based onthe value of the reference picture element; a first decoder for decodinga result of determination showing whether a prediction error is apredetermined value; a second decoder for decoding the codeword for thedecoding picture element whose prediction error is not the predeterminedvalue into the prediction error; a decoding picture element calculatorfor calculating the value of the decoding picture element based on theprediction value calculated by the predictor, the result of thedetermination, and the prediction error obtained by the second decoder,wherein based on information as to which one of the binary symbols is amore probable symbol and an estimated occurrence probability of the moreprobable symbol, at least one of the first symbol restoring device andthe second symbol restoring-device implements decoding for an extendedinformation source of binary symbols effected by selecting a code mostsuited to a state of the extended information source of binary symbolsassumed from the estimated occurrence probability of the more probablesymbol from a set of Huffman codes prepared systematically for theextended information source of binary symbols.
 68. A picture processingapparatus, comprising: a picture pick-up device for picking up a picturecomposed of a plurality of picture elements; a picture compressioncircuit for compressing the picked-up picture; a memory for storing thecompressed picture; and a picture expansion circuit for expanding thestored picture, wherein the picture expansion circuit comprises thedecoding apparatus according to claim
 67. 69. An encoding method,comprising: an outputting step of receiving and storing a pictureelement having a value within a predetermined range as an encodingpicture element, and for outputting a value of an encoded pictureelement adjacent to the encoding picture element as the value of areference picture element; an encoding step of predicting the value ofthe encoding picture element, determining whether the prediction iscorrect, encoding the value of the encoding picture element based on aresult of the determination, and for outputting a codeword for theencoding picture element; and an encoding controlling step ofcontrolling an operation of the encoding step based on the result of theprediction made by the encoding step wherein the encoding stepcomprises: a predicting step of calculating a prediction value of theencoding picture element based on the value of the reference pictureelement; a prediction error calculating step of calculating an errorbetween the value of the encoding picture element and the predictionvalue calculated by the predicting step as a prediction error; adeterminating step of determining whether the prediction errorcalculated by the prediction error calculating step is a predeterminedvalue and for outputting a result of determination; a first encodingstep of receiving the result of determination output from thedeterminating step, encoding the result of determination, and ofoutputting the codeword; and a second encoding step of encoding theprediction error calculated by the prediction error calculating stepwhen the prediction error is other than the predetermined value for theencoding picture element to be encoded and of outputting the codewordfor the encoding picture element to be encoded, wherein based oninformation as to which one of the binary symbols is a more probablesymbol and an estimated occurrence probability of the more probablesymbol, at least one of the first codeword allotting step and the secondcodeword allotting step implements encoding for an extended informationsource of the binary symbols effected by selecting a code most suited toa state of the extended information source of the binary symbols assumedfrom the estimated occurrence probability of the more probable symbolfrom a set of Huffman codes prepared systematically for the extendedinformation source of the binary symbols.
 70. A decoding method,comprising: an outputting step of storing decoded picture elementshaving values within a predetermined range and of outputting the valueof one of the decoded picture elements adjacent to a decoding pictureelement as the value of a reference picture element; a decoding step ofreceiving a-codeword, predicting a value of the decoding pictureelement, determining whether the prediction is correct, and of decodingthe codeword into the value of the decoding picture element based on aresult of the determination; and a decoding controlling step ofcontrolling an operation of the decoding step based on the result of thedetermination made by the decoding step, wherein the decoding stepcomprises: a predicting step of calculating a prediction value for thedecoding picture element based on the value of the reference pictureelement; a first decoding step of decoding a result of determinationshowing whether a prediction error is a predetermined value; a seconddecoding step of decoding the codeword for the decoding picture elementwhose prediction error is not the predetermined value into theprediction error; a decoding picture element calculating step ofcalculating the value of the decoding picture element based on theprediction value calculated by the predicting step, the result of thedetermination, and the prediction error obtained by the second decodingstep, wherein based on information as to which one of the binary symbolsis a more probable symbol and an estimated occurrence probability of themore probable symbol, at least one of the first symbol restoring stepand the second symbol restoring step implements decoding for an extendedin formation source of binary symbols effected by selecting a code mostsuited to a state of the extended information source of binary symbolsassumed from the estimated occurrence probability of the more probablesymbol from a set of Huffman codes prepared systematically for theextended information source of binary symbols.